Stoke-on-Trent - Arsenal's English Premiership title challenge has suffered a major setback as they crashed to a shock 1-0 defeat at Stoke following Jon Walters' late penalty on Saturday.
Having missed four of his previous six penalties, Republic of Ireland international Walters showed nerves of steel to slot home with 14 minutes remaining after Laurent Koscielny was adjudged to have handled inside the area.
Leaders' Chelsea's victory at Fulham meant the Gunners now trail Jose Mourinho's team by four points as they made the worst possible start to a month manager Arsene Wenger had claimed in the build-up would define their season.
Arsenal have now won just once in their last eight trips to the Britannia Stadium and, although this was the first time they had come up against Mark Hughes in the home dugout, the game retained the same feisty edge it became famed for when his predecessor Tony Pulis was in charge.
Gunners striker Olivier Giroud was less than impressed after twice appearing to be trod on -- first by Glenn Whelan and then Charlie Adam -- yet both incidents went unpunished by referee Mike Jones.
Wenger's side could have few complaints with the outcome, however, after serving up a sub-standard display which left big question marks hanging over their seemingly faltering title bid.
Arsenal midfielder Mesut Ozil returned to the Gunners' squad after recovering from a dead leg, however the Germany international had to settle for a place on the bench and made little impact when introduced in the second half.
The win continued Stoke's excellent record at home against the big sides as they made the Gunners their latest scalp, having previously beaten Manchester United and Chelsea and drawn with Manchester City.
There is now a six-point cushion between them and the relegation zone.
There has certainly been no love lost between these clubs since the controversial Ryan Shawcross challenge four years ago which left Arsenal midfielder Aaron Ramsey with a broken leg.
Despite Ramsey's absence, it was soon clear the incident was far from forgotten by both sets of supporters as they fervently voiced support for their respective player.
Events on the pitch failed to match the intensity on display in the stands in the early stages and, even when the game's first noteworthy moment came along in the 15th minute, Walters's glancing header which crept agonisingly past the post was adjudged offside.
The visitors' first opening arrived three minutes later when Santi Cazorla created space for himself on the edge of the penalty area only to curl over the crossbar.
As has so often been the case in games between these sides, it was a bruising battle, particularly for Giroud.
The France striker found himself unfortunate to be penalised for a challenge in which he was left in a heap after being caught by Whelan's studs before being poleaxed by Erik Pieters.
Peter Crouch spurned a golden opportunity shortly after the restart when, unmarked, he failed to connect cleanly with an Adam free-kick.
It was Crouch who posed the biggest threat at either end and the towering striker could count himself unlucky when his angled header was superbly tipped around the post by Wojciech Szczesny following Marko Arnautovic's inviting delivery.
An even better opportunity came along from the resulting corner as Bacary Sagna failed to clear his lines inside the area and the ball fell invitingly for Geoff Cameron six yards out, only for him to divert it wide.
Adam could count himself fortunate to escape without sanction when he appeared to trample on Giroud and Arsenal's frustration was compounded when Koscielny clumsily handled as Walters attempted to lift the ball over him.
Walters sent Szczesny the wrong way his spot kick and Arsenal wasted a chance to equalise deep into stoppage-time when Yaya Sanogo fired over the crossbar from Alex Oxlade-Chamberlain's cross.