Chelsea's Didier Drogba proved Arsenal's nemesis again on Sunday when he scored the opening goal in the champions' 2-0 win over their London rivals which stretched their lead at the top of the Premier League.
Blackpool also had an afternoon to remember, with a shock 2-1 win at Liverpool, which left Roy Hodgson's mis-firing side in the bottom three.
In the day's early kick-off Manchester City beat Newcastle United 2-1 to leapfrog both Manchester United and Arsenal and move into second place.
Chelsea, who have beaten Arsenal in their last four league matches, top the table with 18 points from seven games, followed by City on 14, Manchester United on 13 and Arsenal on 11.
Drogba took his tally to 13 goals in 13 appearances against Arsenal with a shot that went in off the post five minutes before the break after Arsenal had dominated much of the opening half.
Alex sealed the win with a blistering free kick late in the game.
Blackpool stunned Liverpool at Anfield with a 29th-minute penalty from Charlie Adam and a second goal at the end of the first half from Luke Varney.
Sotirios Kyrgiakos pulled one back for Liverpool after 53 minutes but the home side, who lost striker Fernando Torres with an injury after nine minutes, could do nothing to save the match.
Manchester City beat Newcastle with a first-half penalty from Carlos Tevez and a 75th-minute winner from Adam Johnson. Jonas Gutierrez had equalised for Newcastle who lost Hatem Ben Arfa with a suspected broken leg after four minutes.