Jonathan Walters scored the only goal of the game from the penalty spot to earn Stoke City a 1-0 win which badly damages Arsenal's title hopes.
The Irishman converted from 12 yards on 76 minutes as the Britannia Stadium once again proved an unhappy hunting ground for Arsene Wenger.
In a turn up for the books, the Potters had more possession than Arsenal in a first half in which they came close through Peter Crouch, whose acrobatic volley on 34 minutes found the side-netting.
Walters had also threatened with a header which flashed past Wojciech Szczesny's far post, while Arsenal's Polish international goalkeeper saved well from Glenn Whelan's powerful drive.
It took until past the half-hour mark for the Gunners to show anything going forward as Tomas Rosicky rolled in Lukas Podolski to thrash over the crossbar, before Santi Cazorla shot tamely at Asmir Begovic.
Wenger introduced Mesut Ozil off the bench in the second period to help instigate an improved Arsenal performance, but it was Stoke who were the side pressing to break the deadlock.
After Crouch and Geoff Cameron had twice combined to create chances for the hosts, Mark Hughes's team were rewarded for their pressure when Laurent Koscielny was penalised for handball in the box.
Walters has a sketchy record from the spot in recent times, but the Potters workhorse stepped up to slot into the bottom corner to score a goal which eases their relegation fears.
Yaya Sanogo ballooned a shot over the crossbar in the closing stages as Arsenal fell four points behind Chelsea at the top of the Premier League table, with difficult fixtures on the horizon.