The big news ahead of kickoff was that John Terry retained the captain's armband for Chelsea and started the match, despite being handed a four-match ban by the FA on Thursday for racially abusing Queens Park Rangers' Anton Ferdinand.
Terry had been cleared to play after delaying his decision on whether or not to appeal his punishment.
Torres then dispossessed Koscielny moments later, leaving him with just goalkeeper Vito Mannone to beat. However, he lost his balance and stumbled to the ground after taking the ball around the Italian stopper.
The Spaniard's eventful afternoon continued on the half-hour as he found the net again, but the goal was correctly ruled out for offside.
Arsenal levelled slightly against the run of play three minutes before the break. Gervinho collected Oxlade-Chamberlain's cut back from the right, before turning inside the penalty area and unleashing a ferocious strike which flew into the top corner of Petr Cech's goal.