Chelsea lost ground in the Premier League title race after being upset 2-1 by Arsenal, enabling defending champion Manchester United to close the gap to five points with a 1-0 victory over Manchester City.
Liverpool, which is tied with Chelsea atop the standings on 33 points, can take the outright lead when it plays West Ham on Monday.
Robin van Persie scored twice in four second-half minutes after Arsenal defender Johan Djourou had scored an earlier own-goal, as Chelsea manager Luiz Felipe Scolari lost his second home match of the season - which his two predecessors never experienced.
The Red Devils had Cristiano Ronaldo sent off but Wayne Rooney's goal clinched victory in the 150th Manchester derby.
Portsmouth lost a 2-0 lead for the second time in three days but, unlike the 2-2 UEFA Cup draw with AC Milan on Thursday, recovered to beat Blackburn 3-2.
Everton's 1-0 victory over Tottenham was overshadowed by the loss of Ayegbeni Yakubu for the rest of the season because of a ruptured Achilles tendon, with strike partner Louis Saha also facing a lengthy layoff due to a hamstring strain.
Consecutive league losses for the Gunners had left Arsene Wenger defending his managerial reputation, but the London derby victory moved them up to fourth with 26 points, seven behind Chelsea, which has now won just once in its past five games.
Arsenal was struggling to compete with bigger, more physical opponents when Van Persie lashed a 59th-minute equalizer into the top corner from what appeared to be a clear offside position.
"I want only tomorrow or after tomorrow for the referee to look at the television and say 'sorry,'" Chelsea manager Luiz Felipe Scolari said. "I don't want three points, I only want this 'sorry.'
"My team after this lost concentration. The offside killed my team. I lost today because one goal is not a goal. One goal changed the game."
If his first goal involved luck, there was none surrounding his second three minutes later. Emmanuel Adebayor headed Cesc Fabregas' free kick to Van Persie's feet, and the Netherlands striker turned to shoot through Frank Lampard's legs and into the far corner.
With Emmanuel Eboue and Abou Diaby on the sidelines, the Gunners were unable for long stretches to compete physically. Emboldened by Chelsea's defensive lapses, they suddenly looked more like the side that beat Manchester United on Nov. 8 rather than the one which lost has lost to Manchester City, Aston Villa and Stoke this month.
"It's a massive win for us because we had just lost two games," Wenger said. "To lose today would have put us 13 points adrift. It would have been too much."
Chelsea has taken just one point at home against the other members of England's so-called "Big Four" and has to visit Manchester United, Liverpool and Chelsea in the second half of the season.
In Manchester, Rooney ended a six-week goal drought as the European champions took on their neighbors for the first time since Man City was bought by a wealthy group from the United Arab Emirates
The England striker tapped in his 100th club goal in the 42nd after goalkeeper Joe Hart had spilled Michael Carrick's shot from a tight angle.
"We needed to win the game because we are behind Liverpool and Chelsea, so it was a significant result for us," United manager Alex Ferguson said. "I love the type of goal Wayne scored. Andy Cole was a specialist at it. Wayne anticipated the situation very well and I am delighted with that.
"It is a marvelous achievement for him to get 100 goals. His work rate was phenomenal today."
The Red Devils, who played the last 22 minutes with 10 men, clung on to their slender advantage despite facing a far more assertive City in the second half.
Ronaldo was booked for tripping Shaun Wright-Phillips in the 59th. He then sarcastically applauded referee Howard Webb. The Portugal winger was then shown a second yellow card for deliberately handling Rooney's corner.
"He has tried to shield the ball from hitting his face, and he might get a shove in the back as well," Ferguson said. "He thought he had heard the referee's whistle. But I'm not going to get into it because we could be here all day."
Portsmouth, which moved up to seventh place, lost its two-goal advantage when Matt Derbyshire and Tugay Kerimoglu scored after earlier goals from Peter Crouch and Jermain Defoe.
Sean Davis struck the winner in the 79th after goalkeeper Paul Robinson did well to block an initial shot from Papa Bouba Diop.
Tottenham lost its first home match under new manager Harry Redknapp, going down 1-0 to Everton.
Darren Bent wasted the home side's best chance in a scoreless first half when he shot straight at goalkeeper Tim Howard in the 41st minute, while Everton's Tim Cahill missed a free header in the 43rd.
Everton scored the only goal in the 51st, when Steven Pienaar turned in Mikel Arteta's pass. Spurs striker Fraizer Campbell had a shot in the fifth minute of injury time that was deflected just wide.
