Match ends, Manchester United 2, West Bromwich Albion 0.
Jesse Lingard scored his first Manchester United goal as Louis van Gaal's side beat West Brom.
Winger Lingard, 22, curled home from the edge of the box early in the second half to give the hosts the lead.
Substitute Saido Berahino missed a superb opportunity to equalise late on when he headed over from close range.
Juan Mata then made the win safe from the penalty spot late on after Anthony Martial was fouled by Gareth McAuley, who was sent off.
The victory keeps Manchester United fourth in the Premier League, while West Brom are 13th.
It was also a first win in three league games for the hosts, who have not conceded in 550 minutes.
'Attack, attack, attack'
Manchester United fans are struggling to warm to Louis van Gaal's defensive style of football, with chants of "attack, attack, attack" heard at Old Trafford during Tuesday's Champions League win against CSKA Moscow.
Only the Baggies had attempted fewer shots (109) than Manchester United (110) prior to Saturday's game, but Van Gaal indicated he had no intention of abandoning his conservative approach by naming two defensive midfielders - Bastian Schweinsteiger and Michael Carrick - in his starting line-up.
The outcome was, perhaps, predictable, as the hosts, for the most part, lacked the creativity to break down their defence-minded visitors. Only one shot on target was registered in the first half, when Martial shot straight at Boaz Myhill.
However, a moment of quality from Lingard changed the game.
The youngster's goal forced West Brom to abandon their cautious approach, opening up more gaps at the back for the home side to exploit, ultimately leading to the moment when Martial got through on goal in stoppage time, causing McAuley to give away the decisive penalty.
A star is born?
Lingard put in a man-of-the-match performance against CSKA Moscow in midweek and he impressed once again.
His goal lifted an encounter that was threatening to end in a dull draw, taking one touch to control a clearing header, before finding the far corner with his second.
Lingard has spent recent seasons on loan at Championship clubs Birmingham City and Derby County, but is now keeping Memphis Depay on the bench. If Lingard keeps up his recent form, the Dutch winger is likely to have to be patient for his next opportunity to stake a claim for a place in the first team.
More needed once again from Rooney
Rooney got the winning goal against CSKA Moscow to move into joint second alongside Denis Law in Manchester United's all-time scorers list with 237 goals.
Yet his return in the Premier League this season has been disappointing, with this blank against West Brom extending his record to two goals in 11 games.
The England international lined up just behind Martial and, while he produced one or two moments of quality, he failed to register a single effort on target.
United fans appreciated his efforts, applauding him off the pitch when he was substituted late on, but they will surely be keen for him to start posing a greater threat in the final third sooner rather than later.
Man of the match - Jesse Lingard
What the managers said
Manchester United boss Louis van Gaal tells BBC Sport: "Everybody knows who has played football that the most difficult way to score is against a very defensive team. The space is only on the wings and we have tried to do that.
"The only way you can play against such a defensive, organised team is the way we do it, you need patience. In the second half West Brom are more tired and the chances come. The goal changed the game, we had more space. Then you can see the qualities of Anthony Martial, and we score the second goal out of his actions."
West Brom boss Tony Pulis tells BBC Sport: "After half-time the game opened up and we got more into it but the first goal is poor from us. It's a great finish. After that I thought we got into the game and the chance [for Saido Berahino] - if there's a guy you want it to drop to then it's Saido.
"I'm disappointed for the players - most of my sides don't lack effort and commitment - we've just switched off and been punished. Gareth McAuley [for the red card and penalty] should have stayed on his feet and if the kid scores, the kid scores."
The stats you need to know
- Lingard's strike was the first United had scored from outside the box in the Premier League since December 2014 (Juan Mata v Stoke).
- Since debuting for Manchester United, Juan Mata has been involved in more PL goals than any other player at the club (30).
- United have kept eight clean sheets in the Premier League this season already - they kept 11 in the whole of last season.
- Tony Pulis has lost 11 of his 13 Premier League games against Manchester United (W1 D1).
- Manchester United have lost just one of their last 14 Premier League games at Old Trafford (W10 D3 L1).
Manchester United travel to Watford in the Premier League on 21 November, while West Brom host Arsenal on the same day.
- 1de Gea
- 18YoungSubstituted forJonesat 62'minutes
- 5RojoBooked at 61minsSubstituted forBorthwick-Jacksonat 76'minutes
- 10RooneySubstituted forHerreraat 82'minutes
- 25DawsonBooked at 43mins
- 23McAuleyBooked at 90mins
- 11BruntBooked at 65minsSubstituted forMcManamanat 85'minutes
- 7MorrisonSubstituted forBerahinoat 72'minutes
- 33RondónBooked at 60minsSubstituted forLambertat 72'minutes
- Mike Dean
- Shots on Target
Second Half ends, Manchester United 2, West Bromwich Albion 0.
Foul by Bastian Schweinsteiger (Manchester United).
Stéphane Sessegnon (West Bromwich Albion) wins a free kick on the right wing.
Goal! Manchester United 2, West Bromwich Albion 0. Juan Mata (Manchester United) converts the penalty with a left footed shot to the centre of the goal.
Gareth McAuley (West Bromwich Albion) is shown the red card.
Penalty Manchester United. Anthony Martial draws a foul in the penalty area.
Penalty conceded by Gareth McAuley (West Bromwich Albion) after a foul in the penalty area.
Attempt missed. Juan Mata (Manchester United) right footed shot from the centre of the box is high and wide to the right. Assisted by Anthony Martial with a headed pass following a corner.
Corner, Manchester United. Conceded by Jonny Evans.
Substitution, West Bromwich Albion. Callum McManaman replaces Chris Brunt.
Juan Mata (Manchester United) wins a free kick in the attacking half.
Foul by Claudio Yacob (West Bromwich Albion).
Substitution, Manchester United. Ander Herrera replaces Wayne Rooney.
Corner, Manchester United. Conceded by Jonny Evans.
Corner, Manchester United. Conceded by Gareth McAuley.
Attempt blocked. Michael Carrick (Manchester United) left footed shot from outside the box is blocked.
Bastian Schweinsteiger (Manchester United) wins a free kick in the attacking half.
Foul by Craig Dawson (West Bromwich Albion).
Substitution, Manchester United. Cameron Borthwick-Jackson replaces Marcos Rojo.