Watford’s first Premier League triumph of the 2016/17 season is likely to be added to the list of ‘I was there’ matches for those Hornets fans fortunate to be inside the London Stadium as the final score of 4-2 to Walter Mazzarri’s men does not begin to reflect an astonishing game that probably should have seen even more goals.

From even before Michail Antonio had taken advantage of some lax marking to head the Hammers into an early lead, their opponents had looked vulnerable defensively and a mess at times and so it came as no particular surprise when West Ham doubled their advantage in the 33rd minute; magnificent skill from Dimitri Payet setting up Antonio for his second.

But the Hornets were not the only team looking susceptible at the back, with West Ham’s weaknesses being exposed on more than one occasion during a helter-skelter opening 15 minutes when Odion Ighalo will perhaps feel he should have scored at least once.

But it was the Nigerian international who got his side back into the game, albeit with the help of a James Collins deflection, before a superb first half for the neutral ended with Troy Deeney capitalising on more Hammers haphazardry to net a magnificent equaliser.

Watford were looking more assured at the back at this stage, but their opponents’ shortcomings were to continue on a downward trajectory after the break that saw the visitors turn a deficit into an advantage and take charge of proceedings to the extent they looked capable of adding to their tally every time they went forward in the latter stages.

Etienne Capoue was to be the man to complete the turnaround, continuing his fine scoring start to the season by crashing home a Roberto Pereyra cross, before Jose Holebas netted his first goal for the club with a strike from the edge of the area.

More goals could have followed for the Hornets with Adrian forced to make a good save on more than one occasion, but if Walter Mazzarri’s men can iron out their problems at the back this victory bodes well for the rest of the campaign.

Mazzari made four changes to the starting line-up that was defeated 3-1 by Arsenal before the international break, giving full league debuts to new signings Daryl Janmaat and Pereyra. Craig Cathcart and Miguel Britos also returned as Sebastian Prodl and Adlene Guedioura dropped to the bench, but there were no places in the match-day 18 for Christian Kabasele and Nordin Amrabat.

Slaven Bilic was always going to have make one alteration to the team that went down 3-1 to Manchester City last time out following Enner Valencia’s departure to Everton but, like Mazzarri, he made four.

New signing Simone Zaza went straight into the starting line-up, Payet, as expected, made his first start of the season as did Manuel Lanzini, while Sam Byram also returned. Angelo Ogbonna, Gokhan Tore and Ashley Fletcher dropped to the bench.

Watford looked to be the positive from the opening whistle but they were almost caught out twice within the opening minute. After a Capoue throw from the left had been cleared, Zaza helped the ball on inside the centre circle with an overhead kick, setting Antonio away on the left. He cut inside before hitting a shot which Heurelho Gomes blocked with his legs before the Hornets keeper was forced to go to ground again to deal with Payet’s follow-up effort, which was deflected.

The visitors, who were wearing their all-white away kit, soon had a half chance of their own though, with Ighalo firing into the side netting from the left side of the 18-yard box after tricking James Collins with a trademark chop.

But if Watford were aiming to keep it tight in the early stages, they gave a poor demonstration of showing it in the fifth minute when Antonio was not picked up as Payet played in a corner from the left and the new recruit to the England squad planted a firm header beyond Gomes to give the hosts an early lead.

If that wasn’t disappointing enough from the visitors’ perspective, they almost shot themselves in the foot again when Antonio played a dangerous low ball across the six-yard box and Janmaat, for reasons only known to himself, opted to try and back pass to Gomes from barely six yards, only to see the ball rebound off the near post.

The Hornets could easily have been 2-0 down but moments after the escape in their own area, they spurned a great chance to equalise when Ighalo found Pereyra in space on the left side of the box and, instead of shooting when he had every right to do so, the former Juventus midfielder played the return pass but the visitors’ top scorer last season wanted a first touch and that enabled Arthur Masuaku to help block it behind.

After Lanzini had fired harmlessly wide at the other end, Watford went very close again when, after good work by Janmaat, Pereyra beat Payet and crossed for Ighalo to strike a first-time attempted finish that was blocked by Adrian before Valon Behrami sent the follow-up wide.

The opening to the game had been relentless with both sides seemingly intent on helping the other to score whenever possible, but some of the early sting went out of it after Zaza had picked up the first yellow card for a foul on Britos.

The pace may have lessened but West Ham were still looking threatening on the break, with both Antonio and Lanzini chancing their arm from distance before they were afforded a better opportunity when Ighalo was penalised for a foul on Mark Noble 25 yards out. But the Hornets’ wall did its job and succeeded in repelling Payet’s free-kick.

However, the visitors could do nothing about what the French star did in the 34th minute, although they again did not help themselves.

Payet went to attack Britos on the outside before checking back onto his left, but it was what he did next that was stunning, striking a superb Rabona pass that gave Antonio the simplest of headers at the far post to score his and West Ham’s second.

Payet will get some headlines for the goal, and rightly so, but that should not gloss over Watford’s defending which was again poor as Antonio was allowed a free run to score.

The Hornets were rocking and desperately needed to get a foothold in the game – and it arrived four minutes before the interval when Capoue did well to hook the ball forward to Ighalo, who cut into the area, teasing Byram as he did so before striking a right-footed shot which was deflected off Collins and wrong-footed Adrian to reduce his side’s advantage to one goal.

And by half-time it was to wiped out due to more defending in keeping with the theme of the game - and an audacious finish from Watford’s captain.

It had been a quiet first half for Deeney until a misunderstanding between Collins and Adrian gave him the opportunity to latch onto the Welsh international’s stray header on the left side of the 18-yard box. But what followed next was stunning as Deeney magnificently curled the ball from an acute angle over two Hammers defenders trying to intercept and into the far corner to bring a breathless opening 45 minutes to a 2-2 conclusion at the interval.

Whether they had received a half-time rocket from Bilic during the break or not, the Hammers were the quicker out of the blocks at the start of the second period with Payet sending an effort looping through to Gomes before Lanzini hit another shot wide.

Ighalo responded with a wayward effort at the other end before the game nearly took another twist in the 51st minute when Winston Reid slipped as he went to head a Holebas cross out of play, causing him to direct the ball rather closer to his own goal than he had intended.

But the latest twist was not to be far away as just two minutes later the Hornets turned a two-goal deficit into a 3-2 advantage within 14 minutes of playing time.

Pererya was to be instrumental in the turnaround goal, bursting forward to pass to the supporting Janmaat before receiving the wing-back’s reverse return ball and crossing to the far post where Capoue was in plenty of space, giving him to bring the ball down before lashing it into the roof of the net for his third goal in four Premier League outings this season.

The Hammers tried to lift themselves but they were looking nervous at the back every time Watford attacked them and a bad afternoon for the hosts was to get even worse in the 63rd minute.

Only a last-ditch block prevented Janmaat from having a clean strike on goal, but when the ball was recycled Ighalo pulled it back to the edge of the area where Holebas struck a left-footed shot which beat Adrian’s best efforts to keep it out to make it 4-2 and score his first goal for the Hornets.

Mazzarri had already been preparing a change at the point and duly made it in the 68th minute, replacing Ighalo with Isaac Success while Bilic followed suit as Jonathan Calleri replaced Noble.

But it was the Hornets replacement who almost had an instant impact, being released on the break and taking on and beating Collins before his attempted finish was well kept out by Adrian.

Fletcher replaces Zaza with 13 minutes remaining and within moments of his introduction he was to nod down a delivery for Calleri to send a stooping header against the post, only for the flag to go up for offside.

Mazzarri immediately made his second change as Stefano Okaka came on for his debut in place of Deeney and within seconds the Italian international was to make a dart forward, helping to free up the space for Pereyra to produce a lovely jinking diagonal run that took at least two opponents out of the game and deserved a goal, only for his effort to be diverted behind by Adrian.

From the resulting corner though, it briefly looked like the Hornets had a fifth goal and Okaka had netted on his debut when he stabbed in a knock down from close range, but again it was to be deemed offside.

Okaka’s lively introduction continued with him shooting at Adrian with an angled strike before he was booked for over protesting and then finished making a premature exit after sustaining a hamstring injury, leaving his teammates to see out four minutes of injury time with ten men before they could celebrate that is likely to live in the memory of those of a Watford affiliation for some time.

West Ham United: Adrian; Byram (Tore 85), Collins, Reid, Masuaku; Noble (Calleri 68), Kouyate; Antonio, Lanzini, Payet; Zaza (Fletcher 77). Not used: Randolph, Nordtveit, Obiang, Ogbonna.

Watford: Gomes; Cathcart, Kaboul (Prodl 81), Britos; Janmaat, Capoue, Pereyra, Behrami, Holebas; Deeney (Okaka 78), Ighalo (Success 68). Not used: Pantilimon, Guedioura, Zuniga, Watson.

Attendance: 56,974.

Referee: Martin Atkinson.