Premier League leaders Chelsea beat London rivals Arsenal 2-1 with goals from Spaniards Fernando Torres and Juan Mata on Saturday to maintain their unbeaten start to the season while handing Arsenal their first defeat.
Both Chelsea goals came as a result of Mata free kicks and poor Arsenal defending with Torres out-muscling Laurent Koscielny to volley the European champions ahead at the Emirates Stadium after 20 minutes for his third league goal of the season.
Gervinho equalised for Arsenal three minutes before the break when he turned crisply and fired into the roof of the net for his fourth goal of the campaign.
Chelsea, who started with skipper John Terry as he mulls an appeal over a four-game ban for racist abuse, regained the lead after 53 minutes when Mata's free kick eluded everyone before clipping Koscielny and flying in past keeper Vito Mannone.
The victory lifted Chelsea four points clear at the top, at least until the rest of the programme later on Saturday.
Chelsea manager Roberto Di Matteo told Sky Sports: "I thought we were excellent today and deservedly won the game. From the start to the end we never defended too deep, we tried to take the initiative and go forward and create chances and the game went for us today."
Disappointed Arsenal manager Arsene Wenger said: "We were a bit nervous at the start ... But we should never have lost this game.
"It is sad because we gave the game away at home, we conceded two soft goals on set pieces. They had three shots on target and scored two goals and you cannot concede goals at home like we did today. We gave a lot and the least we deserved was a draw."
Arsenal, who started the day in fifth place after two wins and three draws in their opening league games, came close to saving a point three times but were denied by a great Petr Cech save, the woodwork and a late rash shot from substitute Olivier Giroud.
Cech made an excellent one-handed diving save to deny Lukas Podolski a headed goal after 59 minutes and Giroud, who replaced Podolski after 66 minutes, shot into the side-netting late in the game after going round Cech - to the despair of Wenger on the sidelines.
Koscielny, who had a miserable afternoon, almost made amends but saw a late header come back off the post.
Terry, who on Thursday was found guilty of using racist language towards Queens Park Rangers defender Anton Ferdinand last year, was roundly booed by the home fans every time he touched the ball at first, as was former Arsenal defender Ashley Cole.
But as he has done so often in the past, former England skipper Terry appeared unaffected by his off-field troubles and was wildly applauded by the visiting fans and gave two young supporters his boots at the end of the match.