Defender James Collins scored his first goal for Aston Villa in a 2-1 win to condemn Barclays Premier League leaders Chelsea to a second successive away defeat.
Martin O'Neill's £5million capture from West Ham took advantage of slack marking to head the winner after 52 minutes.
Didier Drogba had given the Blues the lead after 15 minutes but Collins' defensive partner Richard Dunne levelled before the interval.
Chelsea found Villa goalkeeper Brad Friedel in inspired form with a series of excellent saves making amends for gifting Drogba the opening goal.
The kick off was delayed for five minutes after referee Steve Bennett was taken ill and fourth official Keith Friend stepped into the breach.
Villa striker Gabriel Agbonlahor had the first effort on goal and his shot on the turn was deflected wide. But after 15 minutes a rare mistake by Friedel, in his 198th consecutive Premier League appearance, allowed Drogba to put Chelsea ahead.
Drogba fired in a hopeful 30-yard drive but Friedel allowed the ball to bounce over his dive and into the corner of the net. But after 32 minutes Dunne struck for the second successive match to bring Villa back on level terms.
Michael Essien was forced to concede a corner after good link up play between Agbonlahor and Stiliyan Petrov. Ashley Young's centre flicked off the head of Frank Lampard and Dunne was on hand to head home at the far past.
Friedel redeemed himself for his earlier error when tipping over a chip from Deco at full stretch and then made another crucial stop to deny Drogba at point-blank range.
Villa took the lead early in the second half when Collins was left completely unmarked at the far post to power a header past Petr Cech from Young's inswinging corner.