Chelsea took a 1-0 lead in to half-time courtesy of an Eden Hazard penalty having been felled by Laurent Koscielny, but the best action of the half was to be seen on the sidelines.
After a 15 minute delay to kick-off was reportedly caused by the away fans letting off flares, the match began with Chelsea on the front foot. However, a nasty clash involving Alexis Sanchez and Thibault Courtois left the Blues goalkeeper looking out-cold on the ground, and despite having treatement and resuming play, he was later forced off through injury. Petr Cech came on, but the action was only just starting to heat up.
After a nasty tackle from Gary Cahill on Sanchez, Jose Mourinho burst from his seat, only to be confronted by his old foe Arsene Wenger. The Frenchman firmly pushed Mourinho in the chest before referee Martin Atkinson and fourth official Jonathan Moss split the pair and gave them clear warning.
The game was lit up when Hazard picked up the ball midway through the first half. The Belgian spun on the spot, saw off the challenge of Santi Cazorla and jack Wilshere before Koscielny brought him down. While the defender was lucky to escape with a yellow, Hazard dusted himself off to convert the spot kick and give the blues the lead.
Arsenal found a way of stopping the prolific Costa for all of 78 minutes, but it made no difference.
They did not go down by six, as happened last season, but one would have been enough and it fell to Chelsea’s man of the match to deliver it.
With Costa snuffed out for much of the game, Hazard rose to the occasion, winning and converting the penalty that first separated these teams.
He was exceptional, running at Arsenal, committing them, unnerving them every time he got in or around the box.
When Costa did escape the shackles of Arsenal’s back line it was to set up Hazard who arrived later, Frank Lampard style, but shot over the bar with 15 minutes remaining.
And then the moment every Arsenal fan, deep down, had dreaded. Fabregas, playing his first game for his new club in England against the one that made his name, playing the sort of pass that used to define games in the red and white of Arsenal – long and accurate, setting up Costa for a chance that was only ever going to be a goal.
He ran, outstripping Arsenal’s defence before drawing Wojciech Szczesny and lobbing him, deftly, to out the result beyond doubt.
Chelsea go into the October international break five points clear of nearest rivals Manchester City after just seven games.
Arsenal have failed to beat Chelsea in any of their last six clashes in all competitions.
Their last victory at Stamford Bridge came in October 2011, when they won 5-3 with a hat-trick from Robin van Persie.