The hosts improved in the second half though, and set up a nervy finish for Northern Ireland - who needed one point to secure top spot - when Paulus Arajuuri equalised on 87 minutes.
Find out how all the action from Helsinki unfolded with Sports Mole's full text commentary below.
4.00pmGood evening and welcome to Sports Mole's live text commentary of Finland vs. Northern Ireland from Group F of the Euro 2016 qualifiers. After Thursday's victory over Greece, the visitors would finish top of the group with a victory today.
4.06pmThe two sides met in March at Windsor Park, when Northern Ireland ran out 2-1 winners. Lafferty scored two goals in five first-half minutes that evening, before Berat Sadik fired a consolation goal before the final whistle.
4.07pmThe team news has been announced, let's take a look at the lineups...
4.16pmThere are not too many familiar names for the layman in the Finland lineup this evening. Tim Sparv is an experienced midfielder with 49 caps, while Joel Pohjanpalo has scored three goals in six Finland appearances in 2015.
4.22pmNorthern Ireland's attacking hopes will once again be pinned on Kyle Lafferty this evening, and it's easy to see why O'Neill has so much faith in the Norwich City striker. The former Rangers man has netted seven times in Northern Ireland's Euro 2016 qualification campaign so far.
4.25pmLet's take a look at the state of play going into today's fixture. Northern Ireland are three points ahead of Romania in second place. A draw would be enough to secure a top place finish for O'Neill's side this evening.
4.26pmNorthern Ireland could lose tonight and still finish top of the group, but Romania are hot favourites for their clash with the Faroe Islands this evening. Romania will also want to secure qualification tonight, with Hungary (who face Greece this evening) just one point behind them in third.
4.29pmAhead of today's fixture, Northern Ireland captain Steven Davis told reporters that his side are fully focused on preparing for next year's tournament.
"Preparations for France start now and it would be nice to finish the campaign on a high by beating Finland. We want to go out and put on another good performance," Davis is quoted by BBC Sport as saying.
4.34pmFinland and Northern Ireland have met each other on eight previous occasions. Finland have won three times, Northern Ireland four times. Northern Irish fans will be pleased to know that have not lost to their opponents for 12 years - a 1-0 defeat on February 12, 2003.
4.35pmAfter Friday's 3-1 win over Greece, Northern Ireland manager Michael O'Neill spoke of his pride on taking the helm of the international team.
"The players were outstanding. Right through the team, magnificent. It's a privilege to be here, I'm proud to stand here as their manager," O'Neill told BBC Sport.
4.38pmNorthern Ireland's last tournament was the World Cup 1986 in Mexico. That side were drawn in a difficult group alongside Brazil, Spain and Algeria, and were only able to muster a draw against the African side.
4.42pmFollowing their successful qualification campaign, Northern Ireland are now ranked 35th in the FIFA world rankings. Last year, the side were 48th, and in 2012 were ranked as low as 96th.
4.46pmKyle Lafferty has been crucial to his side's success in qualifying. Only Robert Lewandowski (12 goals), Thomas Muller (8 goals) and Russia's Artyom Dzyuba (8 goals) have scored more than the Norwich City man en route to qualification.
4.49pmThe striker is currently behind Cameron Jerome and Dieumerci Mbokani in the pecking order at his club side though, and ahead of today's match Lafferty admitted he may have to leave the club before next summer's tournament.
"The only thing I can do is keep scoring goals for my country and make an impact for Norwich. If it is time to leave I'll take the opportunity," Lafferty is quoted by The Mirror as saying.
4.50pmPREDICTION! With ten minutes to go before kickoff, it's time for a prediction. Northern Ireland have done brilliantly to qualify for Euro 2016, and I think they will get the job of finishing top done today. Finland have had a poor campaign, and have rested a number of experienced players this evening. I'm going for a 2-0 win for the Green and White Army - with Kyle Lafferty to get on the scoresheet after missing his side's last fixture.
4.54pmThe teams have emerged from the tunnel, and the anthems will commence shortly. Can Northern Ireland finish top of Group F?
5 minDavis cuts out a Finnish move and sets up a Northern Irish attack, but the hosts win the ball back.
6 minUPDATE! Romania have taken the lead over Faroe Islands. As it stands Northern Ireland will finish top by one point, but that would change if Finland score this evening.
8minCHANCE! Niall McGinn threads through a superb pass into the box, but it's just a yard ahead of Kyle Lafferty, and the Norwich City man can't quite connect.
10 minNorthern Ireland have settled into the game really well, and the hosts have struggled to take control of possession on the rare moments they have had the ball. Michael O'Neill will be pleased with what he has seen so far.
11 minCHANCE! Big chance for Stuart Dallas! Finnish keeper Hradecky blasts the ball straight at his centre-back Ojala, and the rebound falls to Dallas. The Leeds United winger takes a touch before testing Hradecky, but the keeper recovers to make a save.
12 minSHOT! Corner for Northern Ireland is not dealt with, and the ball falls to Chris Brunt, who fired a vicious strike towards goal. His effort his a Northern Irish attacker on the way to goal, to the relief of Finland's defence. This has been a terrific start for the visitors in Helsinki.
14 minMcNair is receiving treatment following a heavy challenge by Uronen, and the teams can take a moment off.
16 minPaddy McNair is back on his feet, and looks to return to action,
17 minFinland are just starting to see a little bit more of the ball now, but Northern Ireland are doing well to cut out any meaningful attacks.
18 minTim Sparv tries to play in Sadik with a ball into the box, but McGovern is always the favourite to collect the ball.
20 minFinland spend a period passing the ball in their own half, but Stuart Dallas and Kyle Lafferty do a good job to close down the Finnish midfield. The sting has been taken out of Northern Ireland's game in the last few minutes, but the hosts have not really troubled them.
22 minThe ball is pumped into the Finnish box from the right, and Norwood attempts to control the pass, but his touch sends it out for a goal kick.
24 minNorthern Ireland are keeping hold of the ball well, but the hosts are looking a bit more resilient at the back now.
25 minSHOT!Chris Brunt will not believe his luck! Niall McGinn wins a corner for Northern Ireland, which Oliver Norwood takes. Finland's keeper punches it as far as Brunt, who hits another vicious strike, and again it hits a Northern Irishman - this time Chris Baird!
26 minCHANCE! First real opportunity for the hosts, as Tim Sparv attempts a half-volley from the edge of the penalty area, but the experienced midfielder drags his effort wide.
28 minCHANCE! Northern Ireland awarded a free kick in Finland's half. It's taken quickly, and Dallas plays in Brunt down the left. The full-back fizzes a low cross towards Lafferty, but the striker can't connect to the ball.
30 minIt's been an entertaining 30 minutes in Helsinki, and you feel that a goal is on its way.
30 minNorthern Ireland take an inventive free kick, as Norwood plays in Brunt, who crosses into the box, before Finland clear for a corner.
31 minGOAL! Finland 0-1 Northern Ireland (Craig Cathcart)
31 minNorthern Ireland are on their way to the top of the group! Brunt's corner is cleared as far as McGinn, who drives down the right before whipping a ball towards Cathcart at the near post, and the Watford centre-back nods it home.
34 minSAVE! Brilliant stop from Michael McGovern! Finland whip the ball in low towards Pohjanpalo, who connects with a decent shot, but the Hamilton keeper produces a great reaction save to maintain his clean sheet.
35 minWell I said a goal was coming, and Northern Ireland have looked the most threatening throughout. McGovern did ever so well to stop Finland pegging them back immediately though.
5.49pmSo far, so good for Northern Ireland in Helsinki. The team need just one point to finish top, but are currently on course to claim all three. Craig Cathcart's goal gives the Green and White Army a deserved lead, although the hosts woke up in the final 10 minutes before half time.
5.50pmRead how the action unfolded in the first half with Sports Mole's half time report here.
5.51pmUPDATE! Romania have added a second goal before half time in their qualifier at the Faroe Islands, and look to be on their way to France alongside Northern Ireland.
5.52pmNorthern Ireland started the game brightly, but Finland went on to have 54% possession and more shots on goal by the end of the half (7-6).
5.55pmMichael O'Neill's side have looked well organised for much of the first half though, with the forwards and midfield closing Finland down well.
5.59pmAs it stands, Northern Ireland will remain top of Group F by three points. Should Finland equalise, the Green and White army will remain top, but with Romania beating the Faroe Islands, Michael O'Neill's side will drop to second place should they lose today. Romania would move ahead of Northern Ireland on head-to-heads, after taking four points from their two Euro 2016 qualifying fixtures.
46 minRESTART! Northern Ireland get the second half underway.
46 minFinland start on the front foot, as Jalasto runs forward down the right flank before unleashing a shot, but his effort is blocked.
48 minThe hosts have started the second half better than they did the first. Lod finds Pohjanpalo from the right, but Brunt makes a good tackle to win the ball back in the box.
49 minSHOT! Mattila has a go from distance, but a deflection sees the ball land comfortably in the hands of McGovern.
52 minDallas unleashes Lafferty down the right, but the striker has no support and does well to win a throw in.
53 minSUBSTITUTION! First change for Northern Ireland as Conor McLaughlin replaces Paddy McNair at right-back.
54 minPohjanpalo is not having his best game this evening, and the big striker has just hit a tame effort towards McGovern. Northern Ireland need to take control of possession, they have been second best since the break.
55 minChris Baird is receiving treatment following a clumsy challenge by Mattila.
57 minLafferty works hard to win the ball from Lod, and Northern Ireland take the ball. Baird sets up McGinn, who finds McLaughlin outside, but the Fleetwood Town man's cross misses everyone.
59 minLafferty tries to hold the ball up as Dallas makes a move to his left, but Finland win the ball back and clear their lines. The match has become a little bit scrappy in the last few moments.
62 minNorthern Ireland have a free kick as Schuller brings down Baird. The former Fulham man is still on the pitch after taking a knock before, but looks like he is struggling a little bit now.
64 minSHOT! Finland keep the ball well for a few moments as their opponents sit off, and they find Mattila, who hits a tame effort from 30 yards.
67 minBrilliant play from Dallas, who shows some neat skill before finding Davis on the right, but the attack is cut out for a throw by Finland. From the throw, McGinn plays the ball into the box, but his cross finds no Northern Ireland shirts and Finland break.
68 minPukki wins a corner for Finland, but Lafferty clears with a far-post header.
69 minLod deemed to be offside after Tim Sparv launches the ball into the box in the youngster's direction.
71 minSUBSTITUTION! Second change for Northern Ireland, as Niall McGinn is replaced by Shane Ferguson.
73 minDavis wins the ball in the Finnish half before setting up Ferguson on the left, but the Millwall man's cross is cut out and Finland attempt a counter attack, which comes to nothing.
75 minStuart Dallas does well to track back and intercept a cross from Uronen. Finland have seen a lot of the ball in the second half but have not been able to breach Michael McGovern and his defence.
77 minSparv launches the ball forward for Pohjanpalo to chase, but it goes beyond the striker and safely towards McGovern. Finland look like they are running out of ideas now.
79 minSUBSTITUTIONS! Finland replace Schuller with Hamalainen, while Magennis comes on for Lafferty for Northern Ireland.
79 minStuart Dallas puts an inviting cross into the Finland box, but the delivery is cleared.
81 minCHANCES! Jalasto gets a clearance horribly wrong and Magennis nods towards Ferguson. Northern Ireland keep the ball alive, and the winger finds Magennis in the box, but the ball is cut out, only for Brunt to hit the target with a shot from distance.
83 minHamalainen takes the ball from Pohjanpalo before attempting a shot, which McGovern saves, before the midfielder returns the ball in the box - only for his cross to sail wide.
85 minMagennis does well to run into the box and find Davis, who keeps the ball alive before finding Dallas. The Leeds man whips a ball into the box, but Finland deal well with the danger.
86 minDanger for Northern Ireland, as Sparv puts a good ball into the box which Hamalainen nods on, but Jalasto is penalised for a push on Brunt.
87 minGOAL! Finland 1-1 Northern Ireland (Paulus Arajuuri)
88 minAn equaliser, and on the strength of the second half it is deserved for the hosts. Hamalainen heads on towards Paulus Arajuuri - the centre-back - who had stayed forwards, before unleashing a composed finish past McGovern. Can Northern Ireland hold on to their top place finish?
89 minUPDATE! Meanwhile, Alexandru Maxim has added a third goal for Romania over the Faroe Islands. They will win their game, so Northern Ireland must hold on here.
6.52pmNorthern Ireland have done it! Michael O'Neill's side have finished top of Group F, ahead of Romania by one point. His side dominated the first half, but were second best after the break. A good result for Northern Ireland though - a professional job well done.
6.53pmFind out how the match unfolded with Sports Mole's full match report here.
6.54pmThat wraps up Sports Mole's live commentary of Finland vs. Northern Ireland, thanks for your company this evening! Stay tuned for analysis, reaction, and more from the Euro 2016 qualifiers.