It is now a question of waiting for other results but Watford could be promoted to the Premier League within a few hours after they beat Brighton and Hove Albion 2-0 to open up a four-point lead at the top of the Championship.

The Hornets now know that if Middlesbrough lose at Fulham and Norwich City fail to beat Rotherham United, their return to English football’s top table will be secured later this afternoon after earning a club record 13th away win of the campaign in the Football League.

Watford struggled to build quality possession in the first half of the opening period and, not for the first time this season, Slavisa Jokanovic showed he isn’t afraid to make changes. Off went Ikechi Anya to be replaced by Daniel Tozser. Within four minutes it had paid off.

Following a period of pressure from the Hornets, the Seagulls failed to deal with Matthew Connolly's delivery into the penalty area, Odion Ighalo seized onto the loose ball and laid it back to Troy Deeney, who swept a shot past David Stockdale to put the visitors in front.

The Hornets had their chances to make the rest of the after more comfortable, certainly for their wonderful travelling army of almost 3,200 fans, before – and perhaps almost predictably – the game came to a thrilling climax.

First Heurelho Gomes made an instinctive save to thwart Craig Mackail-Smith and then came another of those ‘I was there’ moments as Watford broke on the counter and Deeney set up Matej Vydra to score deep into injury time and spark scenes of joyous bedlam and amongst Hornets staff, players and fans alike.

Even if results do not go the Hornets' way later today, victory against Sheffield Wednesday in the final game of the campaign next Saturday will send them up as champions.

Jokanovic decided to make three changes from the side that beat Birmingham City 1-0 for what all concerned in yellow hope will be the final away game of the season.

The fit-again Connolly came into a three-man defence in a 3-5-2 formation, while Anya and Ighalo also started after coming off the bench against the Blues. Miguel Layun, Vydra and Tommie Hoban dropped to the bench.

Brighton came into the match off the back of a run of form that has seen them take only one point from the last available 15 and Chris Hughton made four alterations from the team that lost 2-1 against Wigan Athletic in their last outing.

Inigo Calderon, Watford-born Mackail-Smith and Kazenga LuaLua dropped to the bench while Danny Holla was not involved. Their places were taken by Lewis Dunk, Chris O’Grady, Jake Forster-Caskey and Beram Kayal.

Following an impeccably observed minute’s silence in memory of the victims of the Bradford City fire, the Seagulls came flying out of the traps and it took a good defensive block from Gabriele Angella to prevent O’Grady having a clean strike at goal inside the opening 50 seconds.

The high-tempo opening to the exchanges continued with the Hornets also not hanging around and they had a good chance to take the lead from their first opening in the seventh minute. The ball broke for Deeney on the right side of the penalty area but his shot from a fairly tight angle was blocked by the legs of goalkeeper David Stockdale.

Soon after though, Mustapha Carayol stayed onside as he momentarily broke away down the right before checking back inside Anya and cutting the ball back to the edge of the penalty area where Joe Bennett struck a first-time shot not too far wide of Heurelho Gomes’ left-hand upright.

The Brighton fans, rather than the players, were appealing for a penalty in the 13th minute when Bennett sought to latch onto a long ball over the top and went down in the 18-yard box under pressure from Juan Carlos Paredes, but referee Keith Stroud immediately signalled his lack of interest in awarding a spot-kick.

The Seagulls continued to have the majority of the possession, without threatening too much, while their opponents were too often resorting to playing hopeful balls forwards. Indeed, by the midway point of the first half Jokanovic had already decided his side needed to get more control in the centre of the park and Tozser was introduced as a 25th-minute replacement for Anya as Watford switched to four at the back.

Almost immediately the Hornets began to build some sustained pressure in and around the Brighton area and when the Brighton backline failed to deal with Connolly's whipped in ball from the left, Ighalo laid it back to Deeney, who shifted it out of his feet before driving a low shot past Stockdale to put the Hornets 1-0 up and in an even firmer position at the top of the table.

Almen Abdi had a shot from outside the 18-yard box saved before the hosts almost got back on terms in the 34th minute when a mistake in the Hornets defence allowed O’Grady to fire in a right-foot shot, but Gomes was equal to it, pushing the effort around his near post.

The home side continued to try and look for a way back into the contest, but the Hornets held firm as Bennett picked up the game’s first yellow card three minutes before the break for pulling back Abdi.

There was almost a worrying moment for the visiting defence in first-half injury-time when Angella, presumably because he got a shout, let a clipped ball forward go over his head. Gomes safely gathered, but not before an opponent had darted in front of him seeking to get on the end of it as Watford took their 1-0 lead into the break.

Abdi saw a left-footed effort deflected behind off a teammate a minute after the restart before a majestic touch from Deeney set Adlene Guedioura away down the right, but his cross was cut out before it could reach the unmarked Ighalo coming in at the back post.

Tozser whipped a left-footed free-kick from 25 yards over the top as the Hornets maintained their positive start to the second half and this almost resulted in another goal in the 54th minute. A Paredes cross from the right fell for Guedioura on the edge of the area, he managed to wriggle away from an opponent but lost control of the ball, only to knock it into the path of Ighalo. He shaped to go round Stockdale, but saw the ball nicked off his toes by Guedioura, whose shot was deflected wide of the near post. From the resulting corner on the left, Ighalo flashed a header over the target.

Watford were largely in control and looking to turn the screw though, and Hughton decided to shake things up on the hour when he brought on Mackail-Smith for Carayol.

Cathcart was booked for bringing down O’Grady a minute later before Brighton had a rare sight of goal after the break when Gordon Greer headed a deep corner wide.

Vydra was already waiting to come on while that set piece was being taken and he replaced Ighalo in the 65th minute before Angella sent Mackail-Smith tumbling on the right side of the 18-yard box, earning him a yellow card as a result.

Brighton had enjoyed a reasonable spell but Watford had another opportunity in the 68th minute when Abdi struck a dipping half-volley over the top from the edge of the area after a Vydra pass had broken for him.

The two combined again soon after, but this time Abdi curled a shot across goal and narrowly wide from the left front edge of the 18-yard box.

After Lewis Dunk had headed a long throw into the arms of Gomes, Watford’s next opportunity came when Guedioura again went rampaging down the right, his cut back was missed by Vydra but Deeney hit it on the half-turn, only to see his effort deflected behind.

LuaLua replaced Forster-Caskey with 12 minutes of normal time remaining and then Calderon came on for the injured Bruno as the home side still pushed to get something from the contest, but without creating a clear-cut opportunity.

Fernando Forestieri replaced Abdi in the 81st minute as the prospect of the Hornets opening up a four-point lead at the Championship summit continued to move tantalisingly closer.

But there were hearts in Hornets mouths two minutes later when Calderon’s dinked cross from the right was met by the head of O’Grady, but his downward effort drifted a yard or so wide of Gomes’ left-hand post as the keeper scrambled across.

As the tension continued to rise, Deeney was booked for clattering into Bennett and from Dale Stephens’ resulting free-kick, O’Grady looped a header well over the top. Another opening for the home side followed soon after when Calderon’s low ball in from the right was met by Stephens, but he could only steer his shot into the grateful arms of Gomes.

Guedioura was the next to be booked as the game entered the first of five minutes of injury time for a late challenge on Dunk – with Brighton appealing for a red as the centre-half appeared to be caught by an elbow – before Stephens suffered the same fate for attempting to pull back Forestieri.

Next…the let off.

Gomes charged out of his six-yard box to claim a ball and got a partial block on it but it rebounded to Mackail-Smith, who appeared to have the majority of an unguarded net to steer it into. He made a good enough contact but then Gomes’ arm appeared from almost nowhere to block it.

And next…joyous bedlam.

With Brighton pushing forward in numbers, Deeney put his foot down to reach a ball that was going out of play on the right touchline near halfway. Vydra had already sensed the opportunity and was clear infield, Deeney spotted him and the Czech striker took one glance over his shoulder as he broke into the penalty area, brought the ball under control and then calmly steered it beyond Stockdale to score the Hornets’ 90th goal of the season and earn a potentially priceless three points as promotion moved within touching distance.

Brighton & Hove Albion: Stockdale; Greer, Halford, Dunk; Stephens, Kayal; Bruno (Calderon 79), Carayol (Mackail-Smith 60), Forster-Caskey (LuaLua 78), Bennett; O’Grady. Not used: Walton, Hughes, Best, Ince.

Watford: Gomes; Angella, Cathcart, Connolly; Paredes, Abdi (Forestieri 81), Watson, Guedioura, Anya (Tozser 25); Ighalo (Vydra 65), Deeney. Not used: Bond, Layun, Hoban, Motta.

Bookings: Bennett for a foul on Abdi (42); Cathcart for a foul on O’Grady (61); Angella for a foul on Mackail-Smith (66); Deeney for a foul on Bennett (87); Guedioura for a foul on Dunk (90); Stephens for a foul on Forestieri (90); Dunk for a foul on Vydra (90).

Attendance: 28,841 (3,199 away).

Referee: Keith Stroud.