Watford 4 Chelsea 1
Tiemoue Bakayoko was sent off as Chelsea slumped to a second successive heavy defeat.
Bakayoko was dismissed for a second bookable offence just after the half-hour mark and Troy Deeney’s penalty put Watford ahead three minutes before half-time.
With Olivier Giroud on for his Chelsea debut, Eden Hazard scored a brilliant equaliser with eight minutes remaining, cutting in from the left and firing in from 25 yards.
But the Hornets responded with three goals in the final seven minutes.
Daryl Janmaat slotted home after cleverly exchanging passes with Roberto Pereyra, Gerard Deulofeu’s shot deflected in off Gary Cahill, and Pereyra made it four with an emphatic finish after being set up by Abdoulaye Doucouré.
It came five days after Chelsea were beaten 3-0 at home by Bournemouth – and it left them just a point ahead of rivals Tottenham in fourth place.
And it will no doubt increase speculation over the future of boss Antonio Conte.
Bakayoko was having a woeful game before being dismissed.
Having given the ball away several times, he was trying to win it back after after again losing possession when he fouled Richarlison and picked up a second booking.
Worse followed for the visitors when Deeney scored from the spot after Thibaut Courtois was adjudged to have brought down Deulofeu despite the keeper appearing to make little, if any, contact with the Spaniard.
Giroud was sent on in the second half, replacing the injured Pedro, for the striker’s first appearance since his move from Arsenal.
It enabled Hazard to drop into a deeper role he immediately looked happier in, and his cracking goal seemed to have rescued Conte’s side, only for them to then fold in spectacular fashion.
Chelsea: Courtois; Azpilicueta, Luiz, Cahill; Moses, Bakayoko, Kante, Zappacosta; Willian (Fabregas 34), Hazard, Pedro (Giroud 63).
Subs not used: Caballero, Rudiger, Emerson, Drinkwater, Hudson-Odoi.