Chelsea suffered a Christmas hangover on Friday as they crashed to a 4-2 away defeat to London rivals Charlton Athletic.
The defeat was especially costly for Claudio Ranieri's expensively assembled team as title rivals Arsenal had earlier cruised to a Thierry Henry-inspired 3-0 home victory over bottom-ranked club Wolverhampton Wanderers.
Chelsea, who began the day in joint second place with Arsenal on 39 points, fell behind in the first minute to Hermann Hreidarsson's header. Although Ranieri's side were soon level through John Terry's header, they never looked comfortable.
Matt Holland restored Charlton's lead with a thumping header from Jonatan Johansson's cross after 35 minutes and Johansson made it 3-1 just after the break, tapping in after some brilliant work by Paolo Di Canio.
Jason Euell stunned Chelsea with a fourth after 53 minutes and Eidur Gudjohnsen's goal was purely academic as Chelsea slid to their third league defeat of the season.
Unbeaten Arsenal were simply a class above Wolves, with Henry the tormentor-in-chief. The Frenchman's corner was turned in by Wolves defender Jody Craddock after 13 minutes and when he converted a pass from captain Patrick Vieira seven minutes later the Gunners were threatening to run riot.
Wolves held out until the 89th minute, but Henry struck again with a low shot past Michael Oakes to send Arsenal top of the league.
Manager Arsene Wenger said he was pleased with the result after three draws in their last four games. "We felt we didn't play our best against Bolton and wanted to put that right today," he told Sky Sports. "We were sharp and dominated the game for 90 minutes."
In the day's other early kickoff, Fulham moved into fourth place thanks to Louis Saha's double in a 2-0 home victory against Southampton.
Leaders Manchester United, who have 40 points, can regain the top spot when they play Everton at Old Trafford later today.