Arsenal pulled Chelsea back into the Champions League dogfight as they claimed a 1-0 win over their London rivals.
Emile Smith Rowe's first-half goal consigned Thomas Tuchel to just his second defeat since taking charge at Stamford Bridge.
It also ensured Chelsea failed to give themselves breathing room in a battle for the top four that also features Leicester, West Ham and Liverpool.
See who stood out from the game below.
With the forwards in front him struggling, the Englishman took on the creative burden, and was at the heart of the hosts' best moments.
Only a crowd of bodies and a good save from Bernd Leno prevented him from scoring in the first half.
A momentary lapse of concentration resulted in the midfielder almost passing into his net and, though Kepa Arrizabalaga reacted well, he could do little more than set up a goal.
At this level, it only takes one small mistake to decide a game.
In an Arsenal team that has struggled in creative terms this season, he was all too happy to take on the responsibility, dribbling in tight spaces, and getting his head up constantly.
He also worked his socks off, as summed up by a sliding tackle that stopped a Chelsea attack in its tracks on the right wing in injury time.