Manchester United slipped to their third consecutive defeat as they lost 3-1 at Watford in the Premier League on Sunday.
Etienne Capoue's fourth goal of the season put the hosts in front at Vicarage Road, before Marcus Rashford equalised from close range after the break.
An inspired change by Walter Mazzarri saw substitute Juan Camilo Zuniga sweep Watford back ahead with his first touch seven minutes from time, and Troy Deeney added a late penalty after Zuniga was fouled by Marouane Fellaini.
Defeat for United - who lost Anthony Martial shortly before half-time after an earlier clash of heads with Daryl Janmaat - caps a miserable eight days for Jose Mourinho's side after they were beaten in the Manchester derby last Saturday and then in the Europa League by Feyenoord on Thursday.
It is the first time Mourinho has lost three games in a row as a manager since August 2006, when he was in his first spell at Chelsea.
The hosts - who have beaten United for the first time in 30 years - started quickly and Odion Ighalo squandered a golden opportunity to open the scoring after a mix-up between David de Gea and Chris Smalling presented the Watford striker with an open goal, but he somehow fired wide.
De Gea then saved well from Deeney before United carved out their first opportunity, only for Zlatan Ibrahimovic to shoot wide from six yards.
Paul Pogba, playing alongside Wayne Rooney and Fellaini in a midfield three, struck the crossbar with a superb long-range effort but just as the visitors were growing into the game, Watford went in front.
Martial was robbed of possession on the edge of his own box and Janmaat crossed for Capoue, who struck first-time past De Gea.
It was Martial's last involvement in the match too. He was clearly shaken up having been involved in a nasty clash of heads with Janmaat midway through the first half, and Mourinho introduced Ashley Young in his place just before half-time.
United got back on level terms with their first shot on target as Rashford, who kept his place from the Feyenoord defeat, tapped home after Ibrahimovic's cross came back off the unfortunate Valon Behrami.
The expected late United surge never materialised, and the hosts re-took the lead with seven minutes remaining through Zuniga.
The Hornets substitute had been on the pitch 53 seconds when Roberto Pereyra picked him out, and he fired past De Gea to make an immediate contribution.
Frustrations for United threatened to boil over as Rooney, Memphis Depay and Fellaini were all booked in the closing stages, and Watford added further gloss to the scoreline when the latter tripped Zuniga in the penalty area.
Referee Michael Oliver pointed to the spot and Deeney made no mistake, blasting down the middle to wrap up Watford's second league win of the season.
Player ratings
Watford: Gomes (6), Cathcart (7), Prodl (7), Britos (6), Janmaat (6), Pereyra (7), Behrami (7), Capoue (8), Holebas (7), Deeney (7), Ighalo (7)
Subs used: Success (6), Amrabat (7), Zuniga (8)
Man Utd: De Gea (6), Valencia (6), Smalling (5), Bailly (4), Shaw (6), Pogba (5), Fellaini (5), Rashford (6), Rooney (4), Martial (5), Ibrahimovic (5)
Subs used: Young (6), Depay (6), Mata (6)
Man of the match: Etienne Capoue