A debut goal from Zat Knight and a late Gabriel Agbonlahor strike saw Aston Villa end Chelsea’s 18-match unbeaten streak in the league.
Knight climbed above Didier Drogba to head in a Gareth Barry corner in the second minute of the second half.
Chelsea threw everything at Villa in the final half hour but came up against a determined Villa backline.
Salomon Kalou dragged a shot wide before Villa broke and Agbonlahor stabbed in Ashley Young’s driven cross.
It was a frustrating afternoon for Jose Mourinho at Villa Park, where Chelsea have not won since 1999.
Emmanuel Adebayor’s penalty and Cesc Fabregas’s close-range effort put Arsenal in first-half control.
Rival investment groups from China and Dubai were reported to be preparing £1bn takeover bids for the Premier League champions.