The Tractor Boys were forced to defend for large spells of the game, but with five minutes of added time on the clock the substitute midfielder tucked the ball beyond Heurelho Gomes to seal a dramatic 1-0 victory for his side.
Despite the late setback, which came on the back of a match limited on clear-cut chances, Watford remain in the division's automatic promotion zone.
Relive how the 90 minutes of action at Vicarage Road unfolded with Sports Mole's live text coverage below.
The Hornets are looking to regain top spot in the league table this afternoon, while the visitors will be hoping to push on from their first win in five last time out. We have now well and truly entered the final straight in the race for promotion, with just eight games left to play this term, so a positive result in Hertfordshire could prove all the difference come the end of the campaign.
Starting with the home team, then, and Slavisa Jokanovic has opted to make three changes to his side for this afternoon's clash. Daniel Tozser, Miguel Layun and Odion Ighalo all come into the starting lineup, while Gabriele Angella, Gianni Munari and Matej Vydra drop out for the Hornets.
Fernando Forestieri is not available for today's game having picked up a knock, while Almen Abdi and Sean Murray miss out with reoective hamstring and knee injury problems. Matthew Connolly, brought in from Cardiff City on loan earlier this week, misses out on the squad despite being granted the green light to feature.
Likewise, Mick McCarthy has made a trio of changes to his side, bringing in Chris Wood, Luke Varney and Kevin Bru. Teddy Bishop, Jonathan Parr and Freddie Sears are the men to make way in the starting lineup, as the Tractor Boys aim to pick up back-to-back wins and climb up the table.
Bishop misses out on the squad completely having picked up a shin injury last time out, while the knock sustained by Parr in the victory over Bolton Wanderers means that he is not a part of the 18-man travelling party. Meanwhile, David McGoldrick (thigh), Luke Hyam (knee) and Darren Ambrose (hamstring) remain on the sidelines.
It is a decent looking bench named by the home side, with the the aforementioned Vydra joining Scotland wing-back Ikechi Anya among the backups. The visitors can call upon Sears, Stephen Hunt and Paul Anderson in attack, meanwhile, in what should be a real end-to-end contest at Vicarage Road.
Well Watford may have dropped down to second place following Bournemouth's resounding victory over Middlesbrough a little earlier, but they come into this game as the division's in-form team. Five wins from their last six, with the other game in that run ending in a draw, has seen the Hornets establish themselves among the favourites to go up automatically from the Championship this season.
The division remains awfully tight as we head into the final stretch of games, and as witnessed in that 3-0 win at the Goldsands stadium, alongside Wolverhampton Wanderers's 2-0 win over Derby County last night, every last point - and goal - counts for everything at this stage. With that in mind, Jokanovic's charges will be eager to add some more points to the board prior to the international break by picking up a win over their fellow promotion candidates this afternoon.
Ipswich have suffered some shaky form since the turn of the year, although their win over Bolton in midweek ensures that they remain within touching distance of the playoffs. In fact, a win here today will see them climb back into the playoff zone with Brentford currently 2-1 down at home to Millwall elsewhere in the Championship.
DID YOU KNOW? Ipswich have lost five of their last six games on the road, by far the worst tally of any of the sides chasing promotion, while Watford have taken maximum points in six of their last seven at Vicarage Road.
PREVIOUS MEETINGS: The Blues won the reverse meeting 1-0 at Portman Road earlier this season, but that has proved to be somewhat of an anomaly. That is because they have claimed just two wins from the last 20 games against today's opponents; Watford winning eight of the last nine in all competitions.
We have seen a really fluid start to this game, with both sides looking to wrestle control of the ball. Layun and Motta have particularly seen a lot of possession, without creating any real openings for their teammates.
Ben Watson swings in a dangerous-looking cross into a central position, although Smith is able to clear away to prevent the chance coming to anything. Let's just hope the game remains this open for the remainder.
Just a reminder - Watford are currently second in the Championship table following results elsewhere earlier today, while Ipswich are sitting just outside the playoff zone. A win for either team really would make a huge difference in the race for promotion.
Varney slots the ball beyond Gomes and into the back of the net, but he was adjudged to have been in an offside position having been slipped in by Murphy. Replays show that the officials got the call spot on.
Watford are looking as strong as ever on the counter-attack, and after Motta swung in a cross from out wide Deeney was close to heading home, only to drag it wide of the target. Still no major chances as of yet, with that Guedioura shot a little earlier pretty much as close as we have come to a breakthrough goal.
We are experiencing a quiet spell at the moment, with Watford continuing to take control of the game overall. They have been well matched by the visitors up until this stage, however, unable to truly test Bialkowski between the sticks.
Well following that frantic opening period to the game its been awfully quiet. Both managers are right to the edge of their technical areas at the moment, screaming out instructions to their players. A goal for either side will help this contest to open up a little more.
Deeney is fed the ball inside the Ipswich box, yet he cannot quite get it under control and the opportunity goes begging. He has been a little quiet so far, being restricted to that one headed chance which he dragged wide of goal.
A really sad sight at the moment as Ekstrand lays on the ground following a horrible landing. It appears as though he has broken his leg, so there is no question that Watford will be forced into a change, but in the long term he will be a big loss.
Well following some lengthy treatment on the field, understandably so, Esktrand is carried down the tunnel on a stretcher to a round of applause from every section of the ground. There will of course be a lengthy period of stoppage time at the end of this half as a result
WATFORD SUB: Angella is the man to replace Ekstrand at the back. Can either side now find their rhythm following that lengthy break in play? In truth there wasn't too much flow before that incident anyway.
BLOCK! Guedioura is given time and space to get a shot in at goal, which Murphy brilliantly slides in to block away. The Hornets midfielder may have been better off playing in one of his better-positioned teammates on that occasion.
This has been far from a classic in truth. Some goalless draws are often a misrepresentation of events on the field, but this has certainly been worthy of its 0-0 scoreline heading into the break. Both teams need to step things up following the restart.
It has been a half of very few chances, the best of which arguably fell to Guedioura shortly before the interval. He opted to shoot, seeing his shot brilliantly blocked by Murphy who was sliding in, instead of playing in the unmarked Deeney. In terms of shots on goal, there has been just one so far - Gomes turning aside Varney's drive.
There was a nasty injury picked up by Ekstrand in the opening 45 minutes which led to the hefty stoppage at the end of the half. He appeared to break his leg following a nasty fall on the back of a rather innocuous challenge, almost certainly bringing to an end his season.
This man has been relatively quiet so far, being restricted to just one headed chance which he failed to make the most of. Can Deeney, and indeed the rest of the Watford side, improve their performance in the second half?
RESTART! We are back underway in Hertfordshire, with both sides remaining unchanged following the interval. Angella was of course introduced in the first half, while Ipswich have a full array of subs to choose from.
We have started the second half in the same way the first ended, with a rather scrappy battle. If ever a game needed a goal, it's this one. Let's just hope one of these sides can find a breakthrough soon.
Both teams are still being restricted to the odd long-range attempt and crosses from out wide, which just don't seem to be getting us anywhere fast. Which manager will roll the dice first in this second half?
Both teams are still living off scraps with nothing of note to report back on whatsoever. The incentive is certainly there; Watford needing the points to go top and Ipswich likewise to claw into the playoff zone. At the moment it appears as though we are heading towards a goalless draw.
WATFORD SUB: Jokanovic is the first to blink, introducing attacking full-back Anya in place of Tozser. A nice proactive alteration from the Hornets boss, not for the first time this season, but will it pay off?
Bialkowski's sliced clearance allows Watford to put together an attack, and Deeney signals to the crowd behind that goal to get behind the side. The atmosphere has been as flat as the performance thus far.
A good spell of pressure from Watford comes to an end when Layun overhits a cross towards the back post. Prior to that Mings produced a decent tackle to win the ball from the same man, with the Hornets perhaps turning the screw a little now.
SHOT! The initial set piece was poor, although the return ball came back into the box where it was worked well to Guedioura at the back post. He put his foot through it on the volley with a shot that ended well wide in the end, with Deeney screaming at his teammate for not squaring the ball... not for the first time this afternoon.
This is certainly the best spell of the game for Watford, but even still they have yet to test Bialkowski in the Ipswich goal. At a risk of stating the obvious, that simply has to change in the next 20 minutes or so if Watford are to reclaim top spot.
Watford are still the side on top, looking to keep up this spell of pressure, yet Ipswich don't look all that troubled at the back. In fact, they will be quite happy if the game continues like this for the remaining 20 minutes no doubt, with a point a good outcome in the grand scheme of things.
SAVE! At long last, a goalkeeper is forced into making a save! Having defended well for large parts of this second half, Ipswich almost pulled off the ultimate smash-and-grab through substitute Sears, whose shot from range was creeping into the bottom corner if not for the strong hand of Gomes to turn it aside.
CHANCE! Best opening of the game so far by a clear margin. Watford's attack pairing of Deeney and Ighalo linked up, the former crossing for his teammate in a central position, but he seemed to connect almost too well with the ball from a few yards out and sent it over the bar. It was at an awkward height so it was hardly a sitter, yet he should have done better from there.
It has taken the best part of 80 minutes but this game has finally burst into life. Both teams have come close to making a breakthrough over the past few minutes, with that Ighalo chance in particular looking as though it was going to provide the potentially decisive moment.
Tabb shoots well over the bar from distance when he had Mings in a good crossing position out wide. The full-back was a little unhappy, but you can't blame Tabb for wanting to try his luck when given a bit of space.
Another positive move from Watford is brought to a halt when Guedioura is caught in possession on the edge of the box. He has been involved in almost every piece of attacking play from his side, but more times than not he has proved a liability this afternoon.
Watford remain joint top at the table as we head into additional time at the end of the game, so while this is not the result they would have wanted, it is hardly a disaster. A goal would make them outright leaders heading into the international break, though, which would be a major boost in their promotion hopes.
Ipswich are three minutes away from earning a well-deserved draw at Vicarage Road, which has proved a real difficult ground to come to in recent times. Watford just haven't clicked all afternoon, bar the odd attacking move which they failed to capitalise on.
OH MY WORD!! Ipswich, who have essentially been defending for the best part of 90 minutes, break up the other end with 10 seconds of time on the clock and win the game through Chaplow. It is the classic away performance from the Tractor Boys, Chaplow keeping his cool to tuck the ball into the bottom corner after being picked out by another substitute in Sears.
Absolutely incredible. I said just a minute or so before that winning Chaplow strike that it would be pretty special if Ipswich could go on to win the game having remained so resilient at the back, and they did exactly that with just seconds left on the clock.
Despite the late setback, Watford remain in the automatic promotion zone heading into the two-week international break, while for Ipswich that goal makes the world of difference. Outside the top six all afternoon, they now find themselves level on points with Derby County who occupy fifth place with seven games of the season to go.
Well that concludes our coverage of Championship football for this weekend, and what a cracker it has been. This contest was hardly a classic, but it really came to life in the final 10 minutes or so, culminating in that late Chaplow goal. Until next time, thanks for joining!