Defender James Collins scored his first goal for Aston Villa to condemn Barclays Premier League leaders Chelsea to a second successive away defeat as the home side ran out 2-1 winners.
Martin O'Neill's £5 million 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.
Blues boss Carlo Ancelotti will be frustrated with his side's defending as two corners from Ashley Young presented Dunne and Collins with free far-post headers for the goals.
There was a hint of good fortune about Drogba's goal, with the striker turning well before unleashing a 30-yard strike that Brad Friedel allowed to bounce in front of him without banking on the ball flying up over his dive and into the net.
But after 32 minutes Dunne struck for the second successive match to bring Villa back on level terms, getting on the end of Young's corner to head home, before Collins won it in the second half when he was left unmarked in the box, from where he headed in another corner from Young.