Robin van Persie missed a penalty on his return from injury as Manchester United lost their third successive Premier League game in a frustrating 1-0 defeat to West Brom.
A combination of Chris Brunt and Jonas Olsson struck the decisive blow shortly after the hour at Old Trafford on Saturday, with the Albion skipper's 20-yard free-kick taking a wicked deflection off his team-mate to leave David de Gea helpless.
Van Persie had the chance to level in the 72nd minute when Saido Berahino was adjudged to have handled Antonio Valencia's cross inside the box, but the Dutchman - making his first start since mid-February - saw his spot-kick saved by Boaz Myhill.
As was the case in their defeats at Chelsea and Everton over the last fortnight, Louis van Gaal's team could not make their domination of the ball count.
United were camped in West Brom's defensive third for much of the contest, but were simply unable to break Tony Pulis' stubborn visitors down and Brunt's fortunate effort condemned the hosts to a third loss in a row for the first time since 2001.
Van Gaal's side remain in the box seat to secure fourth spot and a place in the UEFA Champions League, but their poor form has left the door ajar for Liverpool, who now sit four points behind United after beating QPR earlier in the day.
The pattern of the game was set from the off, with United dominating the ball and West Brom defending deep, just as they did to foil Liverpool last weekend.
Van Persie tested Myhill with a scuffed shot, and the returning striker could have opened the scoring in the 19th minute when he flashed a first-time effort narrowly wide from Ashley Young's low cross.
United continued to probe but, with Van Persie understandably rusty after his lengthy lay-off and Wayne Rooney playing in a more withdrawn role, they struggled to carve out clear-cut chances against a typically well-drilled Pulis side.
The second half began in much the same vein as the first, with Rooney having United's first attempt on goal with a 25-yard pot-shot that Myhill gathered easily.
But it was West Brom - victors at Old Trafford last season - who broke the deadlock completely against the run of play, when Olsson unwittingly deflected Brunt's free-kick - which appeared to be going well wide - beyond De Gea.
United were gifted a golden opportunity to level shortly after, but Myhill made an excellent stop low to his left from Van Persie's penalty.
Myhill was in outstanding form, and was again on hand to deny Van Persie and substitute Angel di Maria in the closing stages, but West Brom stood firm as United continue to stagger towards Champions League qualification.
