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Javi Gracia admits he is facing a race against time to fix Watford's season following a third straight defeat.
Record signing Sebastien Haller scored a brace to secure West Ham's first three points of the campaign with a 3-1 victory at Vicarage Road.
Gracia's side are rooted to the foot of the Premier League, having now lost seven successive matches in all competitions for the first time in two decades.
Gracia signed a new four-and-a-half year deal last November, but Watford's latest defeat heaps further pressure on the under-fire Spaniard.
Asked if he was worried about his Watford future, Gracia said: "It is true. What can I say? The dynamic is not good and we need to improve. I know that.
"I am preparing for the next game. We have three days to prepare for Coventry in the Carabao Cup and it is one week before we face Newcastle in the Premier League.
"These games are important, and that is what I am focused on."
Watford's afternoon got off to the worst possible start when Abdoulaye Doucoure fouled Manuel Lanzini in the area after just 59 seconds.
West Ham captain Mark Noble made no mistake from the resulting spot-kick.
Andre Gray, deputising for the injured Troy Deeney, hauled the hosts level with 17 minutes gone.
But Gracia's men were punished for spurning a host of chances, with just three of their 23 shots on target.
Will Hughes should have put the Hornets ahead in the second half only to fire Gray's cross wide of Lukasz Fabianski's goal.
"It is true that there were some moments in the game where we dominated and created chances, but if you have 23 shots and only three of them are on target, it is difficult," added Gracia. "We need to be more clinical. We had one clear chance with Will and it was impossible to miss.
"We've been punished for all the mistakes we've made and it's a difficult moment. We need to change the momentum."
West Ham capitalised on Watford's wastefulness with Haller, the £45million summer arrival from Eintracht Frankfurt, scoring his first goals for the London club in nine second-half minutes.
Felipe Anderson popped up on the left-hand side and his perfect cut-back found Haller, who could not miss from six yards. The French striker then doubled his tally with a neat bicycle kick after Ben Foster tipped Michael Antonio's header on to the bar.
"It is a new league for Sebastien and it is not easy to play in the Premier League from the beginning," said Hammers boss Manuel Pellegrini.
"These goals will give him a lot of trust. I trust him a lot that he will have a positive impact on this league."
Jack Wilshere did not travel to Watford, but Pellegrini said the midfielder was not injured and will play for West Ham in their Carabao Cup clash at Newport on Tuesday.
