Juan Mata was sent off as Manchester United's top-four hopes suffered a setback with a 1-0 defeat at West Brom on Sunday.
The Spaniard received two yellow cards in quick succession in the first half for preventing West Brom from taking a quick free-kick and then tripping Darren Fletcher.
United held out until the 66th minute but their resistance was eventually broken when Salomon Rondon fired home.
The defeat sees United remain three points behind fourth-placed Manchester City in the Premier League having also played a game more, while West Brom move up to 11th.
Four victories in a row in all competitions had raised United's spirits but Louis van Gaal still made four changes from the side that won against Watford in midweek, with Chris Smalling and Michael Carrick among the players to return to the starting XI.
United saw plenty of the ball in the early stages but it was West Brom who looked the more threatening side.
Craig Dawson headed wide after climbing above Anthony Martial and Chris Smalling blocked a shot from Saido Berahino.
The visitors struggled to create many chances of note at the other end and they suffered a setback midway through the half as Mata was dismissed.
The Spaniard was firstly booked for stopping West Brom taking a quick free-kick by sticking his leg up and then shown a second yellow minutes later for tripping Fletcher and with the man advantage, the Baggies stepped up the pressure.
Dawson went close with a ambitious long-range half volley that flew just wide of the post with David de Gea scrambling back before Stephane Sessegnon shot at the keeper.
United managed to regain their composure as the half wore on and then started brightly after the break.
Marcus Rashford saw a shot deflected narrowly wide after good work from Martial and Jesse Lingard then shot onto the roof of the net after cutting in from the left.
But United, perhaps feeling the effects of being a man down,, could not maintain their pressure and fell behind in the 66th minute.
Substitute Sebastien Pocognoli put in a good cross from the left that Rondon controlled and then fired past De Gea.
The introduction of Memphis Depay in place of Rashford failed to jump-start the visitors and West Brom's lead was rarely threatened as United struggled to create any chances in the closing stages, a stony-faced Sir Alex Ferguson pictured in the stands at the final whistle.
Player ratings
West Brom: Foster (6), Dawson (7), McAuley (7), Olsson (7), Chester (6), Sessegnon (6), Yacob (6), Fletcher (7), Gardner (7), Rondon (8), Berahino (6).
Subs used: McClean (5), Pocognoli (7), Sandro (5).
Manchester United: De Gea (5), Darmian (5), Smalling (7), Blind (6), Rojo (6), Ander Herrera (6), Carrick (6), Lingard (6), Mata (4), Martial (6), Rashford (5).
Subs used: Depay (5), Schneiderlin (5), Fosu-Mensah (5).
Man of the match: Salomon Rondon.