A contentious goal from substitute Lukas Podolski allowed Arsenal to beat Stoke City 1-0 at the Emirates Stadium on Saturday.
The Germany international's 78th-minute free-kick was deflected into the Stoke net off defender Geoff Cameron at a time when an Arsenal player was in an offside position.
But the goal was allowed to stand and the win moved the sixth-place Gunners to within a point of Everton and Tottenham Hotspur, the two clubs directly above them.
Arsenal manager Arsene Wenger made five changes to the side that had drawn 2-2 at home to Liverpool in mid-week and two of those were enforced by injuries suffered by defenders Thomas Vermaelen and Kieran Gibbs.
That enabled a recall for France centre-back Laurent Koscielny and an instant debut for transfer deadline day signing Nacho Monreal, the Spain left-back who reportedly cost £8.3 million ($13.2 million, 9.7 million euros) from Malaga.
Stoke had also shared a 2-2 draw in mid-week, at home to Wigan Athletic, and manager Tony Pulis made two changes, restoring Ryan Shotton and Andy Wilkinson to his starting line-up.
Arsenal made a lively start but Stoke made sure they always had plenty of men back and limited the home side to a series of long-range efforts that were either off-target or blocked by defenders.
Eventually the pressure was converted into clearer opportunities and Stoke had goalkeeper Asmir Begovic to thank on three occasions before half-time.
Alex Oxlade-Chamberlain should have scored from the first one, however, as Stoke uncharacteristically made a mess of clearing Jack Wilshere's corner.
The ball fell to the teenager right in front of goal but his shot was right at the goalkeeper.
Bosnia-Herzegovina international Begovic then made a smart stop at his back post to keep out Koscielny's header, before palming away another shot from Oxlade-Chamberlain after Wilshere had set him up with a fine defence-splitting diagonal ball.
Stoke's Jon Walters was hurt in an aerial challenge with Monreal but played on following the application of a huge bandage.
The second period mirrored the first as Arsenal dominated possession but could not convert it into clear chances and Wenger made a double change in the 68th minute when Podolski and Santi Cazorla replaced Oxlade-Chamberlain and Abou Diaby.
The change worked as Podolski finally broke the deadlock from a free-kick 12 minutes from full-time after Andy Wilkinson had been booked for fouling Walcott on the edge of the penalty area.
The former Cologne player saw his shot deflected past Begovic by Cameron but a raised flag halted the home side's celebrations.
Referee Chris Foy consulted one of his assistants, who had spotted that Walcott was offside when the kick was taken.
But Foy ruled that the England forward had not been interfering with play and awarded the goal, to Stoke's clear annoyance.
Cazorla fired a good chance to make it 2-0 over the bar before Koscielny was hurt by a sliding challenge from Ryan Shawcross in the final minute.
Stoppage time also saw a flare-up between Stoke substitute Michael Owen and Arsenal captain Mikel Arteta.