Watford missed the chance to do the double over West Ham for the first time as Andre Ayew's second-half strike secured a 1-1 draw at Vicarage Road.
Ghana international Ayew struck on 73 minutes to notch his first goal since Boxing Day, and only his second goal for the Hammers, who clung on for a point after Michail Antonio's dismissal for two bookable offences four minutes from time.
Troy Deeney's third-minute penalty, his eighth goal of the season, had given Watford a deserved half-time lead but an assured first-half display was overshadowed by a serious injury to Mauro Zarate, who was taken to hospital for scans on his knee.
The result sees Watford rise to 12th in the table while West Ham climb a place to ninth.
An unchanged Hammers outfit got off to the worst possible start when stand-in right-back Cheikhou Kouyate clumsily brought Zarate to ground inside the area after two minutes.
Deeney made no mistake with the spot-kick, rifling the ball low past West Ham goalkeeper Darren Randolph.
With their tails up, Watford almost doubled their lead after six minutes but M'Baye Niang's thunderous drive whistled inches over the target.
Overrun in the opening period, West Ham were almost handed a route back into the game in the 11th minute but Miguel Britos' sliced clearance flashed across the face of goal.
That inspired the Hammers as Sofiane Feghouli pinched possession off Jose Holebas and squared for Robert Snodgrass, whose placed finish was blocked by Younes Kaboul.
Heurelho Gomes was called into action as the half drew to a close, preventing Snodgrass' driven cross from finding Feghouli before parrying Aaron Cresswell's effort away from goal.
The half came to a subdued end as Zarate received 10 minutes of treatment before being carried from the field on a stretcher with a suspected knee injury.
The injury unsettled Watford who, having controlled large swathes of the opening period, found themselves on the back foot after the break against a resurgent Hammers outfit.
Having given away a penalty in the first half, Kouyate was aggrieved not to be awarded one after 50 minutes, but referee Craig Pawson adjudged him to have fouled Niang in the build-up.
The Hammers continued to create chances with Manuel Lanzini's cross-come-shot forcing Gomes into a smart stop before the Watford stopper tipped Jose Forte's header wide.
Antonio spurned a glorious chance to level, heading Cresswell's exquisite cross wide in the 69th minute but he atoned emphatically to provide the equaliser.
After Ayew and Lanzini had combined to release the forward, Antonio raced clear of Kaboul into the Watford area, where he tried to beat Gomes at his near post.
His effort cannoned off both posts before falling perfectly for Ayew who stroked the ball into the unguarded net.
The joy was short-lived for Antonio, however, as he received his marching orders for deliberately handling the ball on 86 minutes.
That swung the game in Watford's favour but the hosts failed to make their man advantage count, substitute Isaac Success missing a gilt-edged chance with the last kick of the game as the spoils were shared.
Watford: Gomes (7), Janmaat (5), Kaboul (7), Britos (6), Holebas (6), Capoue (6), Behrami (6), Cleverley (7), Niang (6), Deeney (6), Zarate (5).
Used subs: Success (3), Cathcart (5), Doucoure (4).
West Ham: Randolph (6), Kouyate (5), Fonte (6), Reid (5), Cresswell (7), Noble (6), Obiang (6), Feghouli (6), Snodgrass (6), Lanzini (8), Antonio (5).
Used subs: Ayew (6), Fernandes (n/a).
Man of the Match: Manuel Lanzini