Arsenal returned to the top of the Premier League with a scrappy 1-0 win at Newcastle on Sunday while Chelsea kept the pressure on the Gunners with a 2-1 defeat of Liverpool to stay in the hunt for the title.
Olivier Giroud ensured Arsenal will start 2014 on top of the standings after ending a personal drought of seven matches without a goal.
Eden Hazard and Samuel Eto'o meanwhile secured a fourth consecutive home win for Chelsea after Martin Skrtel had opened the scoring for the Reds at Stamford Bridge.
Elsewhere, Everton recovered from its first home loss in a year to beat Southampton 2-1 and Tottenham trounced Stoke 3-0.
Third-place Chelsea trails Arsenal by two points and Manchester City by one point. Liverpool, which was topping the standings at Christmas, is six points adrift after a second consecutive loss.
"We believe in ourselves and we are determined to give our best absolutely, and to turn back on this season at the end and think we have given our best," Arsenal manager Arsene Wenger said. "I hope it will be enough, of course, but it's a long way to go. It's too early to say that."
Giroud boosted Arsenal's hopes of winning the title for the first time since 2004 when he scored midway through the second half with a header from Theo Walcott's free kick.
The bad news for Arsenal is that midfielder Mesut Ozil, who missed Sunday's match, is facing a short spell on the sidelines after injuring his shoulder during the win over West Ham on Thursday.
"It is an inflamed shoulder. It should be maybe one more week, maybe less. I don't know, but not a long time," Wenger said.
Wenger's team enjoyed long periods of possession and created several chances early on. But it was unable to convert them before Newcastle almost went ahead toward the end of the first half, when Moussa Sissoko's shot was tipped over by Wojciech Szczesny. Mathieu Debuchy also headed against the bar.
Giroud had a chance to double the lead when Walcott's lob from close range was cleared by Debuchy, but the Frenchman failed to connect properly with the loose ball. Newcastle pushed forward toward the end but Alan Pardew's team slipped to just its second loss in 10 league matches.
Skrtel put the Reds in front from close range at Stamford Bridge after only four minutes, but Hazard hit back in the 17th with a superb strike. Eto'o gave Jose Mourinho's team a decisive lead from Oscar's back pass in the 34th.
Hazard was splendid throughout in his playmaker role, while Chelsea's defenders did a good job of containing Luis Suarez, who was reunited with Branislav Ivanovic for the first time since he bit the Serbian defender on the arm last season and was banned for 10 games.
Eto'o was lucky to escape punishment for an early challenge on Jordan Henderson that led to Skrtel's opener. Late in the game, Eto'o appeared to foul Suarez in the box but Chelsea boss Jose Mourinho defended his striker's physical approach to the game.
"For some weeks I have been criticizing him a lot internally for his failure to adapt to what the Premier League is in terms of physicality, so if he had a tackle deserving of a card it was my fault because I'm asking him to adapt to this," Mourinho said. "On the other situation with Suarez I would resolve this differently with a yellow card for Luis Suarez (...) Sometimes he tries too much... Eto'o just put his body in front of him. It looks like somebody shot him."
Chelsea reacted immediately after Skrtel's opener as Hazard saw his effort saved before Gary Cahill headed wide from Frank Lampard's free kick.
Chelsea's penalty appeals were waved away by referee Howard Webb after Hazard appeared to be clipped by Lucas in the box, and Lampard forced keeper Simon Mignolet to tip the ball over with a trademark powerful shot from outside the box.
The home side was rewarded for its pressure soon afterward when Hazard gave Mignolet no chance with a superb curling shot for his eighth league goal of the season. Liverpool then struggled to contain the Blues and Eto'o converted his team's dominance into a goal when he scored from close range from Oscar's pass.
New Spurs manager Tim Sherwood earned his first win at White Hart Lane as Tottenham easily beat Stoke 3-0. Roberto Soldado converted his fifth penalty of the season in the first half while Aaron Lennon and Mousa Dembele added goals in the second.
It was Tottenham's first clean sheet in the league since Nov. 3 and the win puts Spurs level on 34 points with Manchester United at the halfway point of the season.
Three days after its first home loss in a year, Everton bounced back to beat Southampton 2-1 at Goodison Park. The home side took the lead through Seamus Coleman in the ninth minute when the defender slotted into the net from close range.
Southampton battled back and equalized through Gaston Ramirez, who met Adam Lallana's pass with a left-foot shot from outside the box in the 71st minute. But Romelu Lukaku, who came into the game without a goal in five matches, scored the winner three minutes later.