Walter Mazzarri secured his first win as Watford manager as his side came from two goals down to claim a 4-2 Premier League victory against West Ham at London Stadium.
The Hornets had lost their previous three fixtures in all competitions heading into Saturday's clash and Mazzarri's men looked to be heading for another defeat when a headed brace from Michail Antonio put the hosts into a commanding lead - with Dimitri Payet at his best with two spectacular assists.
However, two strikes in the space of five minutes from Odion Ighalo and Troy Deeney respectively levelled proceedings heading into the interval. And Slaven Bilic's side's capitulation continued after the break - Etienne Capoue hammering in a third before Jose Holebas added a fourth.
And despite a late glut of pressure from West Ham, the hosts did not manage to create a clean-cut chance as their second league appearance at London Stadium ended in defeat.
West Ham were boosted by the return of Payet to the starting line-up for the first time this season and the France playmaker would have given the hosts the lead if not for an instinctive stop by Heurelho Gomes - who had previously denied Antonio.
But Gomes could do nothing to prevent Bilic's side going ahead moments later, Antonio stealing in to nod home from Payet's whipped corner - with the help of a deflection from Deeney.
Matters were almost made worse for Watford soon after, Daryl Janmaat inexplicably turning the ball onto the upright of his own goal before, at the other end, Arthur Masuaku did brilliantly to prevent Ighalo netting from close range.
West Ham continued to control proceedings and had their reward just after the half-hour mark, Payet executing a magnificent Rabona cross to the back post, with Antonio on hand to head home his second.
Watford responded well, though, and Mazzarri's side hauled themselves back into the game when Ighalo's strike took a wicked deflection off James Collins - the Nigeria striker's first league goal of the season.
And the visitors' comeback was complete on the stroke of half-time as, after capitalising on a mix-up between Adrian and Collins, Deeney levelled with a precise finish into the top corner.
Watford continued to build momentum after the restart and went ahead after 53 minutes, Capoue thumping a powerful half-volley that Adrian could only turn onto the underside of the crossbar.
West Ham were shell-shocked and Watford wasted no time in taking advantage - Holebas drilling in their fourth from the edge of the area just after the hour mark, though Adrian should have done better with the attempted save.
The hosts looked to forge an immediate response, but would have found themselves further behind if not for a fine save from Adrian to deny substitute Isaac Success.
Watford thought they had a fifth soon after, as Stefano Okaka prodded in after getting on the end of Younes Kaboul's knockdown, but the goal was correctly disallowed for offside.
However, that decision mattered little as the visitors held firm to secure the spoils and condemn West Ham to a third league defeat of the campaign.