A Didier Drogba hat-trick earned Chelsea a resounding victory over Watford.
The Ivorian opened the scoring from close range on 27 minutes, and soon doubled Chelsea's advantage with a tap-in.
Drogba converted a Geremi cross to seal his hat-trick in the second half, after Andriy Shevchenko had made it 3-0.
The win left Chelsea second on 28 points, three behind Manchester United. Meanwhile Watford dropped to 19th with nine points.
Gabriel Agbonlahor scored with three minutes left to give Aston Villa an unlikely victory in the 'second city derby'.
Villa went ahead through Liam Ridgewell's own-goal, before Mikael Forssell levelled with his head.
Agbonlahor had cleared a Ridgewell header off the line before nodding Ashley Young's cross past Blues goalkeeper Maik Taylor to grab all three points.
The victory moved Aston Villa up to eighth with 21 points, while Birmingham sat 15th on 11 points.