The clinical Frenchman showed his class to score twice in the second-half following strikes from Mark Noble and Andre Gray before the break to claim maximum points in a very entertaining fixture in which the hosts were left to rue missed chances.
Story of the match
Perfect start for Pellegrini
The Hammers made a blistering start to the game and were awarded a penalty within the opening two minutes after Manuel Lanzini was brought down in the box by Abdoulaye Doucoure. The spot kick was dispatched comfortably by West Ham captain Mark Noble on his first start for the club this season, 15 years to the day since his debut for the club.
Watford should have levelled the scoring just minutes later, however Gerard Deulofeu spurned a golden chance in front of goal, firing his effort well over the bar. The Spaniard missed another great opportunity soon after, Issa Diop recovering well to deny the Hornets a deserved equaliser.
Watford net first of the season
After a frantic start, with several chances at both ends, the hosts were eventually rewarded for their efforts on 17 minutes when Andre Gray finished well to make it 1-1.
The heat and the fast-paced tempo began to take its toll towards the end of the first half, Felipe Anderson going closest for the visitors with his header hitting the post shortly before the break.
Watford ‘keeper Ben Foster was forced into action shortly after the interval, and he made a good save to deny Andriy Yarmolenko’s curled shot from distance.
Hornets spurn clear chances
Despite the Hammers’ early chance, the home side should have taken the lead five minutes later; Will Hughes missing an open goal from five yards out, much to the disbelief of everybody inside Vicarage Road.
The second half followed a similar pattern to the first, a very end-to-end game in which both sides felt like all three points were theirs for the taking.
It was West Ham who took the lead just after the hour mark, Anderson passing across the six-yard box to £45m man Sebastien Haller, the club’s record signing finishing with ease to make it 2-1 for his first of the season.
The Frenchman doubled his tally to seal the victory ten minutes later with a great overhead kick finish from close range following a dangerous West Ham corner.
Ismalia Sarr and Danny Welbeck both came off the bench as Javi Gracia tried to salvage a result, however the visitors held on to take all three points.
Three straight defeats for Watford
The Hornets' defeat means they have lost their first three games for the first time ever in a top-flight season.
Defeats to Brighton, Everton and West Ham leaves manager Javi Gracia under pressure, and they travel to Newcastle for their next Premier League fixture.
Mr West Ham shows class
Mark Noble gave West Ham the midfield presence they have been lacking alongside Declan Rice so far this season, and the captain also managed to get himself on the scoresheet.
The Hammers’ stalwart provided some defensive protection in a side that often looks susceptible to counter-attacks, providing energy in the middle of the park and making several important tackles.
Haller off the mark
West Ham’s new talisman netted his first Premier League goal of the season in a very impressive performance.
The Frenchman showed good strength up against Watford’s physical centre backs, and displayed his attacking intelligence with a well-taken brace. He will be very keen to continue that good form throughout the rest of the campaign.