Another woeful defensive performance from Arsenal saw the Gunners pegged back to 2-2 by Schalke in Gelsenkirchen.
The Gunners had taken a 2-0 lead in the first half, thanks to goals from Theo Walcott and Olivier Giroud, but allowed Klaas-Jan Huntelaar to halve the arrears before the break, with Jefferson Farfan grabbing the equaliser as the clock ticked down.
For the opener, Giroud broke clear of the German side's defence before clashing into goalkeeper Lars Unnerstall and Benedikt Howedes. Luckily, Walcott was on hand to scoop up the rebound before slotting home.
Lukas Podolski created the second, getting past defender Hoger before whipping in a cross that Giroud converted with aplomb.
Just when it looked like the visitors would go in with a healthy lead, Santi Cazorla slipped and allowed Lewis Holtby to find Huntelaar. The Dutchman did the rest, firing emphatically past Vito Mannone.
Giroud had a great chance to re-establish the two-goal lead, but volleyed over the bar from a Podolski cross.
With just over 20 minutes remaining, Schalke were level when Farfan - free at the back post - was given far too much time to compose himself before shooting home via a Thomas Vermaelen deflection.
The draw leaves Arsenal second in the table, but just one point clear of Olumpiakos, who beat group whipping boys Montpellier.