There was less than two minutes on the clock when the Brazilian got his first Magpies goal since arriving from Chelsea, albeit a scuffed finish after a skilful turn in the box.
A flowing counter-attack from a Southampton corner provided Kenedy with his second on 29 minutes as Dwight Gayle picked him out for a simple back-post tap-in.
Jonjo Shelvey was every bit as influential as the two-goal midfielder and teed up Matt Ritchie for Newcastle's third in the second half, securing successive home wins.
Relive how the action unfolded on Tyneside with our minute-by-minute updates below.
2.00pmThe term 'six-pointer' comes to mind today as Newcastle United host Southampton at St James' Park, with the two teams sitting directly above the drop zone separated by only one point and one place in the table. Neither side can afford to lose, but will either be brave enough to secure a vital win?
2.06pmRafael Benitez reverts to the same team which claimed the scalp of Manchester United in their previous home game, making three changes from the team which lost to Liverpool last weekend. Christian Atsu, Jordan Murphy and Mikel Merino are out for Ayoze Perez, Matt Ritchie and Jonjo Shelvey.
2.08pmThe return of Shelvey following a knee injury is a big boost to the Magpies as he was finally starting to have a consistently positive infuence on their performances - and results - prior to his layoff. "The penny has dropped", the midfielder admitted after an up-and-down Newcastle career thus far.
2.10pmRitchie was the goalscoring hero against the Red Devils with his one and only goal in 26 league appearances this term. That was almost a month ago now, with Newcastle having only been in action twice since - and failing to win both games - due to their fourth-round exit from the FA Cup.
2.12pmRecalls for Perez and Ritchie at the expense of Murphy and Atsu suggest that Benitez anticipates having a lot more of the ball this afternoon as opposed to playing on the break as they tried to at Anfield. Ritchie certainly adds creativity while Perez will provide Dwight Gayle with more support.
2.14pmThe Toon Army have a new hero in the form of loan goalkeeper Martin Dubravka, who has been very impressive since his deadline day arrival from Sparta Prague, which has solved a real problem for Benitez as neither Karl Darlow or Rob Elliot were proving reliable enough between the posts.
2.20pmOnto Southampton now, who make two changes from the team who were held at a stalemate by Stoke City last weekend. Youngster Josh Sims and Oriol Romeu drop out of the midfield as the double-barrel duo of Pierre-Emile Hojbjerg and James Ward-Prowse return to the starting XI.
2.22pmWard-Prowse had scored four goals in his last seven league games - having previously scored way back in April 2017, before he was axed last time out, which is somewhat indicative of manager Mauricio Pellegrino's occasionally senseless rotation policy. The 23-year-old is back in today.
2.24pmOne position that Pellegrino has not rotated of late is in goal where Alex McCarthy makes his 11th successive Premier League start. Time is running out for Fraser Forster to regain his spot and provide Gareth Southgate with a reminder of his quality ahead of this summer's World Cup.
2.26pmSouthampton are again without Steven Davis and Maya Yoshida because of respective hamstring and knee injuries. Long-term absentee Charlie Austin continues his recovery from a hamstring problem which gives January signing Guido Carrillo another chance to get off the mark for the Saints.
2.28pmAt least Southampton fans have got to see their new striker in action, however underwhelming that has been. Islam Slimani is still unavailable for Newcastle as he nurses the thigh injury that he picked up just before joining on loan from Leicester City. Jesus Gamez is another absentee for the hosts.
2.30pmSTAT:Rafael Benitez's side have scored just 12 Premier League home goals this season - no side has netted fewer. Southampton haven't exactly been prolific on the road though this season, finding the net only 13 times in 14 matches. Strap yourselves in for a thriller today then!
2.32pmIf Newcastle are to find their scoring boots today, then there is an obvious weakness in this Virgil van Dijk-less Saints defence. No side has conceded more headed goals in the Premier League this season than Southampton's 11. Five of the last nine goals they have conceded have been headers.
2.34pmHaving said that, Southampton have also conceded a league-high 11 goals from outside the area this season. So today could be the perfect opportunity for Shelvey to open his account for the campaign!
2.36pmRESULT: Today's early Premier League kickoff focussed on the opposite end of the table, where two goals from Marcus Rashford secured Manchester United a huge win over rivals Liverpool. An Eric Bailly own goal set up a tense finish but United hung on to consolidate second.
2.38pmSo Newcastle have done what Liverpool could not manage this season - beat the Red Devils. That 1-0 win over United is part of a run of five unbeaten home matches in all competitions, having lost their previous five at St James' Park.
2.40pmSouthampton have won just two away games in the league all season - at Crystal Palace and West Brom. However, the Saints have not lost any of their last four away matches, winning one and drawing three - only Tottenham boast a better current run in the Premier League.
2.42pmThat away win at The Hawthorns is Southampton's only league victory in their last 16 matches, a dip in form which has seen them plummet from mid-table safety to the heart of the relegation dogfight.
2.44pmAfter a summer of unfulfilled transfer promises, Newcastle were always expected to be hovering around the drop zone but so far Benitez has done a great job of getting positive results at home against their closest rivals. Palace, Stoke and West Ham have all lost at St James' Park this season.
2.46pmAt this stage of the season, this could be Newcastle's biggest game yet. That's certainly how some of the fans are feeling.
2.48pmDespite these two teams being among the Premier League's lowest scorers, they served up a rather entertaining 2-2 draw in October, when Manolo Gabbiadini bagged a brace for the Saints. The Italian has only scored once since, and is definitely suffering from second-season syndrome.
2.50pmSouthampton have in fact scored in 18 of their last 19 meetings with Newcastle, a run dating back to 2003 when their former striker and Geordie legend Alan Shearer notched in a 1-0 United win.
2.52pmHEAD TO HEAD: Newcastle are on a run of seven games without a victory over Southampton in the Premier League. Their last win against the Saints was at St James' Park in 2013, when they triumphed 4-2.
2.54pmBenitez himself has gone five top-flight encounters without beating the Saints, having started his Premier League career with five consecutive wins over them at either Liverpool or Chelsea.
2.56pmSaints boss Pellegrino actually played for Benitez at Liverpool, briefly, and more notably at Valencia. So it might be friendly on the touchline today, but not on the pitch with so much at stake.
2.58pmPREDICTION: This is likely to be a cagey match decided by who is brave enough to really push for a win in the second half. I expect Southampton to control the game for long periods, but Newcastle to stand firm and strike them with a sucker-punch to pinch it 1-0.
1 minKICKOFF: We are underway on Tyneside, which has greeted Southampton with typically wet and miserable weather!
2 minIgnore everything I said about a cagey start, because Newcastle have scored with little more than a minute on the clock! Shelvey knocks a ball up to the chest of Kenedy, who uses his body smartly to turn Hoedt, before scuffing his left-footed finish beyond McCarthy and just inside the post.
4 minCHANCE! It really should be 2-0 to the hosts, with Shelvey whipping a ball in behind the Saints defence for Gayle, who gets the wrong side of Stephens but his first touch lets him down and McCarthy comes off his line to block.
6 minThis Southampton defence looks very unorganised in the opening stages, with Hoedt and Stephens both being isolated one-on-one and plenty of space in behind for Gayle to run onto Shelvey's passes.
8 minUPDATE: There has been another big goal at the bottom of the Premier League with West Brom taking a 1-0 lead against Leicester. Keep up to date with all of the latest scores in our live results section.
10 minSouthampton string a few passes together for the first time through Lemina, Tadic and Cedric down the right, but Dummett stays with his opposite full-back and thwarts the danger.
12 minCedric's swinging delivery to the back post is excellent but Yedlin gets in front of Redmond at the back post to make his clearing header. The Saints man is goalless in 29 league matches.
14 minThere has been a bit of a nasty streak in the early minutes and Stephens concedes a free kick for clattering into Gayle from behind. Shelvey's delivery is straight down McCarthy's throat.
16 minPerez embarks on a promising run down the Newcastle left but appears to be stuck for ideas when he reaches the box, eventually unleashing a hopeful shot which is blocked by Cedric.
18 minThe visitors are slowly recovering from their nightmare start and are starting to control possession, although they have yet to show much penetration and Newcastle's back four aren't going to be giving them any space to play with, especially now that they have a goal to sit on.
20 minA decent chance for Newcastle to break four-on-four goes to waste as Gayle turns backwards and plays towards his own goal. The Magpies need to continue to be positive, rather than be content to hold what they have and see what happens. There is a long time to go in this game!
22 minDiame is having a really good game so far. He is not giving the Southampton mdifielders any time on the ball, which is important considering the quality that Lemina and Ward-Prowse possess.
24 minCHANCE! More good pressing from Diame sees him pinch the ball from Lemina in the Saints half. Gayle and Perez end up getting in each other's way and that distraction may have been a factor in the former failing to stretch McCarthy with a left-footed shot which is easily saved.
26 minThe ball breaks enticingly into the path of Cedric, who runs onto it but slices a 25-yard shot high and wide. The full-back has not scored in nearly five years, so may have been overreaching there!
28 minSouthampton spread the ball nicely to Redmond who squares up Yedlin on the left side of the box, but a distinct lack of confidence is visible with a nothing cross with Lascelles hooks clear.
29 minA ruthless and beautifully-worked counter-attack puts Newcastle two up before the half-hour mark! It all starts with Lemina slipping on the edge of the Magpies box from a Saints corner, and Perez and Gayle both pick the right passes to tee up Kenedy to tap home from close range.
31 minThe Toon Army are in great noise now, and that is because their team really has given them something to shout about. That goal on the break was Liverpool-esque; pace, precision and vision to set Kenedy up for his second. There has been a distinct lack of all of that at the other end.
33 minShevley wriggles free of Hojberg over by the right byline but cannot pick out a man with his cutback.
35 minThe visitors can't get anything right at the moment. Even the ever-reliable set-piece delivery of Ward-Prowse has escaped them, as an overhit cross is claimed with authority by Dubravka.
38 minDiame continues to put himself about in midfield and is perhaps lucky to escape a yellow card for a barge on Hojberg. He was a forgotten figure in the first half of the season but his partnership with Shelvey has produced Newcastle's best performances and results in recent weeks.
40 minSouthampton are so short of ideas that they must look at Claude Puel's supposedly pedestrian football from last season and look back on it in the same way that Newcastle fans do with the 1995 entertainers. Pellegrino needs to make changes at half time but he isn't usually that proactive.
42 minThe hosts' two-goal advantage looks in absolutely no trouble as we approach the half-time whistle. Southampton have yet to have a shot on target and striker Carrillo has been very quiet.
44 minDubravka has barely put a glove wrong so far in a Newcastle shirt but he is lucky to get away with a weak punch here after needlessly wandering 15 yards off his line from a set piece.
3.52pmThis is one of the biggest games of the season for both teams, but only one of them has turned up and Newcastle deservedly hold a 2-0 at half time, with Kenedy bagging both goals.
3.54pmNewcastle's second was a thing of beauty as Perez, Gayle and Kenedy combined in a flowing counter-attack. Southampton on the other hand have been completely devoid of that sort of inspiration.
3.56pmSTATS: The half-time numbers reflect just how poor the Saints have been going forward, managing only one shot and none on target despite having 67% of possession.
3.58pmLATEST: Elsewhere in the Premier League it is still goalless between West Ham and Burnley, Everton and Brighton and Huddersfield and Swansea, who have Jordan Ayew sent off. The only goals away from St James' have been at The Hawthorns where West Brom and Leicester are 1-1.
4.00pmSUBSTITUTIONS: The players are starting to reemerge and Southampton are preparing two changes. Sims and Long are coming on and Lemina and Tadic are being hooked at the interval.
46 minKICKOFF: After a couple of false starts, Andre Marriner allows the second half to get underway...
48 minYELLOW! Pellegrino does not seem like the hairdyer treatment type but Hoedt has put a marker down for this second half with a vicious thud on Perez as he galloped down the right wing.
50 minThe two Saints changes seem to be intertwined with a switch in system, with Long going up top alongside Carrillo and Sims playing on the right in an old-fashioned 4-4-2. At least Pellegrino is trying something different because his side weren't at the races in the first half.
52 minCLOSE! Perez is afforded a free header at the near post but glances it onto the roof of the net.
53 minSims shows a turn of pace to knock the ball by Lejeune on his way to the right byline, but an unpunished shove from the defender prevents the furious Saints youngster from getting a cross in.
54 minCHANCE! Kenedy, on the hunt for a hat-trick, has way too much time and space to collect Ritchie's pass inside the box and shoot right-footed on the turn, just wide of the post.
56 minRedmond finally shows signs of life by bursting past Yedlin down the left - which is no easy feat - but Newcastle skipper Lascelles come across to block the cross at the near post.
57 minNewcastle are well on their way to a massive three points, with Ritchie grabbing a third goal with a first-time placed shot into the bottom corner from Shelvey's perfectly-timed layoff.
59 minCHANCE! The Saints respond by manufacturing their best chance of the game as Long feeds Sims for a cross which Carrillo turns straight into the hands of Dubravka. It was a good run to the near post from the striker but the finish did not have much behind it.
61 minAs results stand elsewhere, Newcastle would climb to 13th in the Premier League, five points above safety.
63 minThis has been the most complete performance I have seen this season from Newcastle. They have often shown defensive solidity and organisation, and today that has been matched by their attacking ambition and conviction.
65 minCHANCE! Ward-Prowse's corner is into a good area and Betrand of all people is left unmarked in the box, but he cannot direct his header on the stretch under the crossbar.
67 minSUBSTITUTION: Pellegrino plays his final card by bringing on Gabbiadini for Carrillo, who is now eight games without a goal since his £19m arrival. Gabbiadini only has one in 18 himself since his double against Newcastle back in October.
69 minYELLOW! Stephens follows his centre-back partner Hoedt into the book for a frustration-induced push in the back on Perez, off the ball after a free kick goes against the visitors.
71 minSUBSTITUTION: Gayle gets a warm ovation as he jogs off to be replaced by Joselu, who will help Newcastle hold the ball up and relieve any pressure that the Saints manage to apply.
73 minNewcastle striker Aleksander Mitrovic has just scored for Fulham. Some fans thought loaning out the Serbian was a mistake, but based on this performance they need not have worried.
76 minSHOT! Sims has been quite lively since his half-time introduction, and here he cuts inside onto his left foot to let fire a a powerful shot which Dubravka strongly pushes away.
78 minSUBSTITUTION: It has been a great team performance from Newcastle today, but there is a special standing ovation for Kenedy whose two goals have put them on their way to three massive points. Christian Atsu gets a late cameo in place of the Brazilian on the wing.
80 minThe two Newcastle substitutes combine as Joselu holds the ball up and feeds Atsu, who gets by one man down the Magpies left but is halted by a strong tackle from Cedric.
82 minSUBSTITUTION: Merino is Newcastle's final substitute as he replaces Shelvey. The penny may really have dropped with the midfielder, who was a class above his opponents today.
84 minAtsu's cross in towards the near post is nearly turned into his own net by the head of Hoedt.
86 minMerino releases Yedlin down the right but the rapid American can't quite keep the ball in play. There has been absolutely no sign of a Saints comeback, with a Newcastle fourth more likely.
88 minThat is unless Southampton are gifted a goal by a mistake, which nearly happens here as Dubravka gets caught in two minds throwing the ball out and drops it just outside the box. Fortunately for the Magpies goalkeeper, Lejeune is alert to get to the ball before Long or Gabbiadini do.
90+2 minThere will be three minutes of added time here, which will surely end with a huge Toon Army roar.
5.03pmThe final whistle signals a hugely significant victory for Newcastle in their fight against the drop and sends Southampton deeper into the relegation mire. Kenedy's first-half brace sent the Magpies on their way before Matt Ritchie's measured finish sealed the three points before the hour mark.