LONDON — A change of managers at Chelsea but Arsenal still can’t conquer its London rival.
Arsenal was undone by a damaging five-minute spell in the first-half of Sunday’s derby against a Chelsea team unbeaten after a month under Guus Hiddink’s control.
Per Mertesacker was sent off for tripping Diego Costa, then the striker scored the game’s only goal at the Emirates Stadium in the 23rd minute.
"He got Mertesacker sent off," Arsenal manager Arsene Wenger said of Costa. "A fact is a fact, I do not accuse him of anything. It’s just what happened."
Watch match highlights: Everton 1, Swansea 2 || Arsenal 0, Chelsea 1 ||
It's now four years, three months since Wenger figured out how to beat Chelsea, which is on its fifth manager since the 5-3 loss to Arsenal in November 2011.
Arsenal turned its stadium into a fortress this season, remaining unbeaten in the league since the opening day -- until Sunday.
Arsenal dropped from first to third place this weekend, behind leader Leicester and Manchester City, although there are 45 points still to play for.
"We had a mountain to climb with 10 men but I believe even there, there was enough to come out at least with a 1-1," Wenger said. "It's a shame to put such an energy into a game and come away without the point. And overall I felt we gave absolutely everything until the end."
Wenger was jeered by Arsenal fans for replacing striker Olivier Giroud with defender Gabriel after losing Mertesacker.
"You want to make a poll for every decision to see who does what? I made the decision and for me it was quite normal," Wenger told reporters. "We had to go for long distances and we needed pace to go from one goal to the other. We knew we had to drop deeper and use pace to get forward."
For Chelsea, the focus is now on the Champions League and FA Cup.
Since Jose Mourinho was fired last month for turning the champs into chumps, the league campaign has been about restoring pride.
Hiddink has achieved three wins and four draws, but Chelsea is still in the lower reaches of the standings in 13th place. The fourth Champions League place, occupied by Tottenham 14 points away, looks unobtainable.
Everton is a point and a place above Chelsea after losing 2-1 to Swansea in Sunday's other game.
Gylfi Sigurdsson put Swansea in front from the penalty spot in the 17th minute and, after Jack Cork's own goal levelled the game, Andre Ayew netted before halftime to give Francesco Guidolin made a winning start as head coach of the Welsh club.
Swansea moved four points above the relegation zone.
"I dreamed of working in Premier League but I didn't dream of winning the first match," said Guidolin, the former Udinese coach. "I must understand what happens in this day because I am surprised. It is new for me."