Match ends, Manchester United 2, VfL Wolfsburg 1.
Premier League leaders Manchester United earned their first win of the Champions League group stage as they came from behind to beat Wolfsburg.
With Chelsea and Arsenal losing in the competition on Tuesday, United were in danger of going the same way when Daniel Caligiuri finished off a six-pass move for the opener.
But Juan Mata levelled from the spot, after Caligiuri handled.
Mata then flicked through for Chris Smalling to slide in the winner.
The Bundesliga side went close to an equaliser when former Arsenal striker Nicklas Bendtner saw a close-range shot hit Wayne Rooney.
All four teams in Group B are now on three points after CSKA Moscow beat United's opening-day conquerors PSV Eindhoven in Russia.
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Are United realistic Champions League winners?
Manager Louis van Gaal was adamant United have a "realistic" chance of winning the competition, when asked earlier this week.
They last won the Champions League in 2008 and lost in the final in 2009 and 2011, while Van Gaal won the competition with Ajax in 1995.
The way United were cut open for Wolfsburg's opener - with stand-in right-back Antonio Valencia playing Caligiuri onside - was not the defending of champions.
But the hosts showed plenty of quality from thereon in as they took the game to their counter-attacking opponents, creating numerous good chances and deservedly turning the match around.
Against a Wolfsburg side packed with ability, United grew nervy late on and will know they will have to see out games better if they are to go deep into this competition.
A new Old Trafford hero?
Anthony Martial failed to score in his seven Champions League matches for Monaco last season.
But there was no lack of confidence on show as the 19-year-old's direct style and skill posed Wolfsburg's defence problems throughout.
The £36m summer signing had scored four goals in his first five matches for United, and he went close with a couple of individual efforts in the opening half against Wolfsburg.
He also created a golden opportunity for Rooney - running to the byeline and crossing low for the England striker to prod over - before being denied by goalkeeper Diego Benaglio after another direct run late on.
Experience can prove crucial
A few eyebrows were raised when Van Gaal signed Bayern Munich midfielder Bastian Schweinsteiger in summer, but the 31-year-old's experience could be key for a relatively young United side.
The German was always available to take possession and had more touches and made more passes than any other player on the field before he was substituted on 70 minutes.
It was no coincidence that without the calming influence of Schweinsteiger in the middle, Wolfsburg grew into the game in the last 20 minutes as United struggled to keep the ball.
Man of the match: Chris Smalling
What the manager said
Manchester United boss Louis van Gaal: "It was very difficult because they scored so early. Then we did very well, we created a lot of chances. We don't finish it and it was a lucky penalty I think.
"Of course it is a penalty but there are some referees not whistling for that. We have created many more chances - Rooney and Depay could have scored and you finish the game.
"Then we score and after that it was suffering. A lot of players are very tired, but we didn't give much away. How many chances have we given away? Maybe one."
The stats you need to know
- Juan Mata scored his first Champions League goal since December 2012
- Mata has been involved in 14 goals (8 scored, 5 assisted) in his past 21 games for Manchester United.
- United have not kept a clean sheet at home in their past six home games against German sides.
- Wolfsburg have only failed to score once in eight Champions League group games.
- Bayern Munich were the last German team to beat Manchester Utd at Old Trafford in the Champions League. It was in April 2001.
- 1de Gea
- 25A ValenciaSubstituted forYoungat 45'minutesBooked at 79mins
- 28SchneiderlinBooked at 39mins
- 31SchweinsteigerBooked at 41minsSubstituted forJonesat 72'minutes
- 7DepayBooked at 61minsSubstituted forPereiraat 62'minutes
- 15TräschSubstituted forJungat 77'minutes
- 18Costa Santos
- 27ArnoldSubstituted forSchürrleat 70'minutes
- 7CaligiuriBooked at 33mins
- 12DostSubstituted forBendtnerat 70'minutes
- Viktor Kassai
- Shots on Target
Second Half ends, Manchester United 2, VfL Wolfsburg 1.
Chris Smalling (Manchester United) wins a free kick on the left wing.
Foul by Nicklas Bendtner (VfL Wolfsburg).
Attempt blocked. Andreas Pereira (Manchester United) right footed shot from outside the box is blocked.
Hand ball by Naldo (VfL Wolfsburg).
Foul by Anthony Martial (Manchester United).
Josuha Guilavogui (VfL Wolfsburg) wins a free kick in the defensive half.
Attempt missed. Ricardo Rodríguez (VfL Wolfsburg) left footed shot from outside the box is close, but misses to the right from a direct free kick.
Foul by Morgan Schneiderlin (Manchester United).
Julian Draxler (VfL Wolfsburg) wins a free kick in the attacking half.
Foul by Phil Jones (Manchester United).
Nicklas Bendtner (VfL Wolfsburg) wins a free kick in the defensive half.
Foul by Morgan Schneiderlin (Manchester United).
Josuha Guilavogui (VfL Wolfsburg) wins a free kick in the attacking half.
Corner, VfL Wolfsburg. Conceded by Ashley Young.
Foul by Daley Blind (Manchester United).
Max Kruse (VfL Wolfsburg) wins a free kick in the attacking half.
Foul by Chris Smalling (Manchester United).
Max Kruse (VfL Wolfsburg) wins a free kick in the defensive half.