Psychological barrier remains
This was the kind of defeat to bring the self-doubt creeping back in. Arsenal had considered this a glorious opportunity to make a statement against the champions, a side languishing in lower mid-table.
Put Chelsea to the sword and Arsenal would go to the top of the table with a sense of invincibility. Instead, they are third, a team driven to distraction again by their inability to wound these opponents. They have not beaten the Blues in the Premier League since 2011.
Costa torments Arsenal again
The identity of Arsenal's tormentor-in-chief was hardly a surprise, either. Diego Costa has looked more his old self of late, his side-footed finish at the near post was his sixth goal in as many games. He is running eagerly beyond opposing defences again, a snarling threat on the shoulders of centre-halves.
Against Arsenal, the street fighter in him comes to the fore. He had been punished retrospectively for his antics in the win at Stamford Bridge in September , but the sending-off he induced from Per Mertesacker this time appeared justified. Contact may have been slight, but Costa was running at pace, even if the subsequent series of agonised rolls may have been more for effect.
The locals sensed play-acting, though the visiting support merely rejoiced in a chorus of: "Diego Costa, he's done it again." Ultimately, he had.
Sacrificing Giroud backfired
Disbelief swept around the stands as Olivier Giroud was summoned from the fray in the wake of Mertesacker's dismissal. Here was Arsene Wenger sacrificing his leading scorer, a player with nine goals in his last 10 matches, and the only natural front man in his pack.
There was a logic to the decision on the basis Chelsea would dominate the ball and Arsenal's most obvious threat would be on the break where Theo Walcott - captain for the day to celebrate his 10th anniversary at the club - might be key.
As soon as the hosts trailed they were blunted. Alexis Sanchez lacked match fitness while Mesut Oezil and Mathieu Flamini were the most advanced central players. That is never the answer, as they lacked an attacking focal point while chasing the game.
Fabregas revels on a familiar stage
The talk before this game centred on former Chelsea goalkeeper Petr Cech. But it was another player facing his former team who made an impact - Cesc Fabregas.
The Blues midfielder dictated play, constantly collecting possession and slipping passes beyond the home defence.
The Spaniard was constantly on the move, aware and inventive, and had 54 touches before the break, 12 more than any other player.
He should have won a penalty from Laurent Koscielny in the second half, and the fact that he won more tackles at the Emirates than in any other game to date this season is an indication of renewed motivation.