Chelsea's hopes of a third straight Premier League title took a dent on Tuesday when they were held to a 2-2 draw at home by Reading.
Two goals from top scorer Didier Drogba looked like hoisting Chelsea ahead of Manchester United at the top, but an own goal from Michael Essien five minutes from time proved costly.
Chelsea have 46 points from 20 games and United can stretch their lead to four points if they beat Wigan Athletic later on a busy day of holiday fixtures.
Drogba muscled through a crowd to head in Frank Lampard's corner after 38 minutes but Chelsea looked shaky without injured captain John Terry and Reading equalised after 67 minutes when Leroy Lita stooped to connect with Glen Little's cross.
Chelsea went back in front when Drogba headed his 12th league goal of the season from a pinpoint Shaun Wright-Phillips cross five minutes later but Reading rescued a point when Ashley Cole slashed a clearance straight at Essien and the ball flew past Hilario.
Elsewhere, Portsmouth moved up to third with a 2-1 victory at West Ham United while Tottenham Hotspur racked up a 12th consecutive home victory with a 2-1 defeat of Aston Villa.
