London: Chelsea continued their domination of Arsenal with a 1-0 win Sunday that denied the 10-man Gunners the chance to go top of the Premier League.
Diego Costa scored the only goal after Arsenal's Per Mertesacker was sent off at the Emirates Stadium.
Chelsea are unbeaten in nine league games against the Gunners, who would have jumped ahead of Leicester at the top of the table with a win.
The Blues are also unbeaten in seven games since Jose Mourinho was fired last month and move up to 13th place on 28 points.
"It is a big win," midfielder Nemanja Matic said. "It is always hard playing Arsenal in this stadium but I think we deserved to win."
"This win will give us more confidence for the future. Today was the real Chelsea."
Arsenal remain third on goal difference behind Manchester City with both on 44 points, three fewer than Leicester.
"It's a shame to put such an energy level into a game and come out without some points," manager Arsene Wenger said.
"We had a mountain to climb because of 10 men but even there I believe there was enough room there to at least come out with a 1-1."
Mertesacker was shown a red card in the 18th minute for a lunging challenge that took down Costa after the striker was sent in on goal.
"That was a major decision at the start of the game and gave the advantage to Chelsea," Arsenal goalkeeper Petr Cech said.
"The referee made the decision to give the red card and he had a clear view, if there was contact then it was the correct decision because Per Mertesacker was the last man."
Costa added insult to injury five minutes later when he got in front of Gabriel Paulista, who came on after Mertesacker's red card, and swept in a cross from Branislav Ivanovic.
Arsenal have now gone six games without scoring against Chelsea, matching their longest-ever drought against a Premier League opponent set against Liverpool from 1997-2000.
Swansea gave new head coach Francesco Guidolin a victory in his first game in charge by beating Everton 2-1 - the Swans' first-ever win in 22 league meetings with the Toffees.
Gylfi Sigurdson scored with a 17th-minute penalty but the hosts equalized shortly after as Gareth Barry's flick from a corner kick went in off Jack Cork for an own goal.
Andre Ayew then scored the winner in the 34th mintue with a shot that deflected off John Stones and looped over Tim Howard.
"This is a new world for me," Guidolin, who was hired January 18, told the BBC. "My first match in the Premier League and away against a strong team like Everton, to win is fantastic."
Swansea's second straight win moves them four points points clear of the relegation zone up to 15th place.
Everton have one win from 10 in the league and remain 12th in the table.