Match ends, Watford 1, West Ham United 3.
Record signing Sebastien Haller believes that West Ham's opening Premier League victory at Watford can "launch" their season.
Haller, who arrived in a deal worth up to £45m from Eintracht Frankfurt in July, scored twice as Manuel Pellegrini's side consigned the hosts to a third straight defeat this term.
The Hammers, who lost all three of their corresponding fixtures last term are 13th, albeit in a cluster of 10 clubs on four points that goes up to fourth.
The French forward said: "It's really important to get a win. Now it's done, we're really happy with the result and the work from the boys.
"It was time to win a game to launch the season."
Haller, who missed last weekend's 1-1 draw at Brighton, opened his West Ham account with a tap-in from Felipe Anderson's cut-back.
And he then acrobatically turned the ball home with an overhead kick from three yards after following up from a corner.
Mark Noble's third-minute penalty set West Ham on their way to their first win of the season after Manuel Lanzini had been fouled by Abdoulaye Doucoure.
But Watford responded to level with a well-worked Andre Gray goal, with the forward drilling home a right-foot shot from Will Hughes' pass.
However, the Hornets were punished for their wastefulness in front of goal with just three of their 23 shots finding the target.
Javi Gracia's side, who sit bottom of the table, have now lost seven successive games in all competitions for the first time since 1999.
Reversal of fortunes for Watford
At the same stage last term Watford had collected nine points after an impressive start, but a pointless return this time around represents a complete reversal of fortune.
While they did at least register their first goal of the campaign, manager Gracia appears to have problems at both ends of the pitch to contend with.
Despite creating a multitude of opportunities, Gray's 17th-minute strike was all they had to show for their endeavour.
Gerard Deulofeu's influence as a creator was a plus, but he cannot be relied upon to be the prolific forward the club need to improve on last term's 11th-place finish.
The former Barcelona man had seven shots on goal, with only a close-range strike that hit the West Ham crossbar finding the target.
It was a chance, alongside Will Hughes' extraordinary miss from a yard out after Gray had squared the ball with the score at 1-1, that summed up the hosts' lack of potency in attack.
At the other end the presence of Haller, Anderson and Lanzini provided too much power, pace and guile for the Watford defence to cope with.
Gracia's side now face a challenging sequence of fixtures - with a home game against Arsenal sandwiched between trips to Newcastle and reigning champions Manchester City - having shipped 41 goals in their last 18 matches.
Haller takes centre stage
Having arrived at West Ham after impressing at Utrecht and in the Bundesliga, there is a certain amount of expectation surrounding Haller.
But his first two goals and overall performance suggested that he has the attributes to justify his club record price tag.
The 25-year-old led the line in exemplary fashion and contributed to all three West Ham goals.
His work to chase down possession led to Lanzini winning the penalty that delivered their opener.
The former France Under-21 international then displayed his predatory instincts, holding his run to ensure he was well positioned to capitalise on Anderson's break down the left.
That allowed him to comfortably claim his first goal for Pellegrini's side before acrobatically doubling his tally.
"[Sebastien Haller's] goals were two very important goals for him," Pellegrini said.
"Coming to the Premier League is not easy. He had just one start in a difficult game against Man City, for a striker the most important thing is to score."
Man of the match - Sebastien Haller (West Ham)
Noble joins esteemed company - the stats
- Watford have lost four league matches at home in a row for the first time since a run of five between October and December 2013 in the Championship.
- West Ham are undefeated in their last four away matches in the Premier League, winning three of those (D1) - they'd lost seven of their previous eight (D1).
- West Ham are the first club to have had as many as 150 different goal-scorers in the Premier League, following Haller's first goal for the club.
- Watford had more shots against West Ham (23) than they managed in their first two games of the season combined (19).
- Watford's Gray has scored 13 Premier League goals since his debut for the Hornets - only Troy Deeney has scored more in this period (14).
- West Ham's Noble has scored five Premier League goals against Watford - more than he has netted against any other side in the league.
- Noble has now scored 25 penalty goals in the Premier League - only Alan Shearer (56), Frank Lampard (43) and Steven Gerrard (32) have scored more in the competition.
Watford host Coventry in the Carabao Cup on Tuesday 27 August (19:45 BST) before they visit Newcastle in the Premier League on Saturday 31 August (15:00 BST).
West Ham visit Newport in the Carabao Cup on Tuesday 27 August (19:45 BST), before resuming their Premier league duties at home to Norwich on Saturday 31 August (15:00 BST).
- 25HolebasBooked at 63mins
- 19HughesSubstituted forSarrat 74'minutes
- 8CleverleySubstituted forQuinaat 86'minutes
- 7DeulofeuSubstituted forWelbeckat 74'minutes
- 21OgbonnaBooked at 76mins
- 7YarmolenkoSubstituted forAntonioat 55'minutes
- 10LanziniSubstituted forC Sánchezat 88'minutes
- 8Felipe AndersonSubstituted forFornalsat 78'minutes
- 15C Sánchez
- Chris Kavanagh
- Shots on Target
Second Half ends, Watford 1, West Ham United 3.
Domingos Quina (Watford) wins a free kick in the attacking half.
Foul by Issa Diop (West Ham United).
Foul by Domingos Quina (Watford).
Michail Antonio (West Ham United) wins a free kick on the right wing.
Attempt missed. Etienne Capoue (Watford) right footed shot from outside the box is high and wide to the right following a set piece situation.
Danny Welbeck (Watford) wins a free kick in the attacking half.
Foul by Ryan Fredericks (West Ham United).
Substitution, West Ham United. Carlos Sánchez replaces Manuel Lanzini.
Substitution, Watford. Domingos Quina replaces Tom Cleverley.
Attempt missed. Andre Gray (Watford) right footed shot from the right side of the box is too high. Assisted by Tom Cleverley with a headed pass following a corner.
Corner, Watford. Conceded by Issa Diop.
Attempt missed. Arthur Masuaku (West Ham United) left footed shot from outside the box misses to the right. Assisted by Manuel Lanzini.
Attempt saved. Abdoulaye Doucouré (Watford) left footed shot from the left side of the box is saved in the centre of the goal. Assisted by Tom Cleverley.
Attempt blocked. Ismaila Sarr (Watford) right footed shot from outside the box is blocked. Assisted by Danny Welbeck.
Attempt saved. Pablo Fornals (West Ham United) left footed shot from the left side of the box is saved in the centre of the goal. Assisted by Michail Antonio with a cross.
Etienne Capoue (Watford) wins a free kick in the defensive half.
Foul by Sébastien Haller (West Ham United).
Attempt missed. Tom Cleverley (Watford) left footed shot from the centre of the box is just a bit too high. Assisted by Abdoulaye Doucouré.