Romelu Lukaku scored his third goal in four appearances as Manchester United moved back to 11 points behind Premier League leaders Manchester City with Sunday's 2-1 win at West Brom.
Second-placed United have now won six of their last seven Premier League games, but last weekend's 2-1 derby defeat at home to rivals City - who thrashed Spurs on Saturday to make it 16 successive league victories - means their title hopes remain remote.
The desired new manager bounce has failed to materialise at The Hawthorns, despite a late consolation, with Alan Pardew's men set to go bottom if struggling Swansea City win at Everton on Monday.
Lukaku broke the deadlock after 26 minutes - against the club where he scored his first Premier League goals - the Belgium international getting between two defenders to plant home a fine header from a precise left-wing Marcus Rashford cross.
The second United goal came eight minutes later and ultimately proved decisive, Ahmed Hegazi trying to block a Jesse Lingard drive from the edge of the box but only succeeding in deflecting the ball past Ben Foster.
Rashford went close to extending the lead but United's failure to kill the match with a third goal almost proved costly when Gareth Barry scrambled home from a 77th-minute Chris Brunt corner, although Jose Mourinho's men held on.
A blocked Rashford effort was the closest either side came to scoring in a very flat start to the match.
When a shot on target finally came it was the opening goal, as Lukaku scored for the 10th time in the Premier League this season.
United's first incisive attack created space on the left wing for Rashford, who floated in the ideal centre for Lukaku to flick in an unstoppable header, the former Baggies striker opting not to celebrate against his old club.
8 - Romelu Lukaku has had a hand in eight goals in eight @premierleague games against former club West Brom (five goals, three assists). Haunt. pic.twitter.com/x0Lm5fNE8r — OptaJoe (@OptaJoe) December 17, 2017
At the other end a driving run from Oliver Burke on his first Premier League start was stopped by a tremendous Chris Smalling tackle before Salomon Rondon saw a near-post effort well blocked.
And with their second shot on target of the game, United seemingly put the game beyond West Brom.
Juan Mata teed up Lingard on the edge of the box, with the England midfielder's strike giving former United goalkeeper Foster no chance after taking a massive deflection off Hegazi.
Jake Livermore forced David de Gea's first action after 43 minutes, but the Spaniard's save was comfortable, and after the interval an excellent Antonio Valencia clearance prevented Rondon from turning in Burke's cross.
Rashford drilled a decent chance narrowly wide of the far post after 57 minutes when Lingard touched Valencia's centre on to his England colleague, and the Ecuadorian then limped off, allowing Marcos Rojo to make his 100th United appearance.
United seemed to be cruising to a ninth win in 12 trips to West Brom, but the hosts scored their first goal in four matches under Pardew's leadership from a set piece with 13 minutes to go.
Former United defender Jonny Evans won the first ball from a Brunt corner and Barry was on hand to slot home his first goal for West Brom from close range to set up an exciting finale.
Substitute Jay Rodriguez headed another dangerous Brunt corner wide with six minutes to go and United suddenly looked nervous, but Mourinho's men clung on despite a late aerial barrage.
Key Opta Stats:
- Manchester United have won their last three away Premier League games, one more than they managed in their previous 10 on the road (2).
- West Brom are now winless in 16 consecutive league games – the longest run in their entire league history (D8 L8).
- Romelu Lukaku has been involved in eight goals in his last eight Premier League games against former club West Brom (five goals, three assists).
- Lukaku has scored 10 goals in his last 11 Premier League appearances at the Hawthorns, a run which spans games with West Brom, Everton and Man Utd.
- Gareth Barry's goal was his first as a substitute in the Premier League since April 1999 (for Aston Villa against Nottingham Forest), a gap of 6,812 days.