Ajax Amsterdam came from a goal down to beat Manchester City 3-1 on Wednesday and leave the Premier League champion facing a major battle to reach the Champions League knockout stage.
Samir Nasri fired City ahead from James Milner's pass midway through the first half but the Dutch side leveled on the stroke of halftime when Siem de Jong crisply dispatched Ricardo van Rhijn's cross from the right.
Defender Niklas Moisander guided in a corner to establish Ajax's lead on 57 minutes and there was no way back for City when Christian Eriksen's shot took a deflection off Gael Clichy to wrongfoot Joe Hart 11 minutes later.
Borussia Dortmund tops Group G on seven points from three games after beating Real Madrid 2-1. Real has six points followed by Ajax (three ) and City (one ).
Arsenal, Real Madrid outclassed
In Group B, Schalke 04 became the first non-English team to win at Arsenal in a European tie for nine years as goals from Klaas-Jan Huntelaar and Ibrahim Afellay earned a 2-0 victory to put them top of the table.
Dutchman Huntelaar rifled a shot past Vito Mannone with less than 15 minutes remaining to give the German side the lead that their impressive performance deserved.
Arsenal, which had won its opening two games in the group, was subdued throughout as Schalke, semifinalist two seasons ago, carved out the better chances.
Afellay then sent the home fans heading for the exits when he sealed victory late on.
Schalke tops the group with seven points with Arsenal in second on six.
Borussia Dortmund leapfrogged Real Madrid at the top of Group D after outclassing the nine-time European Cup winner 2-1.
Poland striker Robert Lewandowski fired the hosts into a deserved 36th-minute lead in front of a sellout 65,000 crowd following a poor pass from defender Pepe.
Injury-hit Real bounced back two minutes later with a delicate lob by Cristiano Ronaldo over keeper Roman Weidenfeller from the edge of the box.
Dortmund then went back in front with a sweet, first-time shot from defender Marcel Schmelzer in the 64th minute after a weak punch by Real keeper Iker Casillas, who had made a string of superb saves to keep his team in the game.
Malaga stuns Milan
Champions League debutant Malaga stunned seven-time winner AC Milan when Joaquin made up for missing a penalty with the winner in a memorable 1-0 Group C victory.
After Kevin Constant brought down Jesus Gamez on the edge of the area, former Spain winger Joaquin drove his 44th-minute spot kick high toward goal but it skimmed the top of the crossbar and flew into the crowd.
However, he made no mistake in the 64th minute when played through by Manuel Iturra; his low shot beat Milan goalkeeper Marco Amelia and went in off the post to give Malaga an impressive three wins out of three.
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