Liverpool scored twice in the opening 18 minutes to beat Chelsea 2-0 on Saturday and further dent the champions' aspirations of a third successive title.
Leaders Manchester United, on 57 points, can open a nine-point lead over second-placed Chelsea, beaten for the third time in the league, if they win at Arsenal on Sunday. Liverpool, third on 46, moved within five points of Chelsea and four clear of Arsenal. Liverpool, beaten 4-1 by Chelsea in the corresponding fixture last season in October 2005, took just four minutes to go ahead.
Peter Crouch glanced Jamie Carragher's long ball out of defence into the path of Dirk Kuyt and the Dutch striker rounded Paulo Ferreira and steered the ball past keeper Petr Cech, playing for the first time since a serious head injury in October.
Liverpool went two up in the 18th minute with a superb strike from Jermaine Pennant, scoring his first goal for Rafa Benitez's side since arriving at Anfield last July.
Steven Gerrard's cross from the left into the middle was headed out by makeshift centre back Michael Essien straight to the unmarked Pennant on the right. The winger chested the ball down, let in bounce once and struck a dipping right-footed volley over the diving Cech and into the top far corner off the underside of the crossbar.
"We're in there and we just have to keep hoping other (teams) keep slipping up," said Liverpool captain Gerrard, whose team have won eight of their last nine league games.
John Arne Riise brought a fine early save out of Cech, who wore a skull cap for his first match since a nasty knock at Reading on October 14 resulted in a fractured skull and surgery.
Just past the hour, Riise let rip with one of his trademark long-range thunderbolts that struck the bar and went up in the air with the Czech Republic keeper then diving to save Crouch's poor header.
Two goals down midway through the first half, Jose Mourinho brought on Shaun Wright-Phillips for winger Arjen Robben after the Dutchman appeared to twist an ankle landing badly.
That substitution and Andriy Shevchenko coming on for the ineffectual John Obi Mikel in the 73rd minute did nothing to change the game for Chelsea. the London side have been rocked lately by rumours of Mourinho's departure and a string of injuries and suspensions to key players including captain John Terry.
"When a team is very fragile on the pitch and mentally, this makes them not so self-confident," Mourinho told Sky Sports.
A messy free kick in the 68th minute summed up Chelsea's day when Didier Drogba tapped the ball between Michael Ballack's legs while the German had his head turned looking where he might pass it.
Kuyt could have had a second goal in the dying minutes but he volleyed Gerrard's pass over the bar from close in.