Santi Cazorla fired 10-man Arsenal to a 1-0 win at Sunderland on Saturday, but the Gunners' triumph was marred by Jack Wilshere's thigh injury.
Although Arsene Wenger's side moved up to fifth in table, keeping the pressure on Tottenham, who won 2-1 earlier in the day at home to Newcastle, as the north London rivals continue their battle with the leading pack for a place in next season's Champions League.
However, there was immediate reason for concern over England midfielder Wilshere, who limped off in the second half following a strong challenge from Alfred N'Diaye.
And the dismissal of Carl Jenkinson made it an uncomfortable finish for Arsenal, whose victory would have been far more comfortable if not for the inspired form of Sunderland goalkeeper Simon Mignolet.
Mignolet made two fine saves inside the opening two minutes from Theo Walcott as Martin O'Neill's back-four was unlocked with an ease that was surprising for a team possessing one of the best defensive records in the Premier League.
Sunderland, meanwhile, did force Arsenal goalkeeper Wojciech Szczesny into action when he dealt with an angled drive from Stephane Sessegnon after an incisive run by the forward.
Arsenal continued to look the more impressive side, throughout an opening half as their passing and movement gave them the edge over their more pedestrian hosts.
The difference was plain to see when Wilshere cut through Sunderland as Arsenal constructed one of their best moves of the half in the 32nd minute.
It finished with Aaron Ramsey's shot that swerved wickedly and required Mignolet to make his best save of the match to turn it away at full-stretch.
But even Mignolet was unable to do anything about the goal that gave Arsenal a deserved lead four minutes later.
Wilshere was again involved with a determined run before Walcott took over, setting up Cazorla for a fierce low finish beyond Mignolet.
O'Neill's response was to send on Sebastian Larsson in place of captain Lee Cattermole as another reminder to his skipper that his value to the team is being affected by his disciplinary record.
Arsenal also had to make a significant change five minutes into the second-half when Wilshere was hobbled off to be replaced by Abou Diaby.
They were not disrupted by the loss of Wilshere as Olivier Giroud was again close to a goal with a 55th minute shot at the end of another inventive move.
A rare Sunderland break that climaxed in Steven Fletcher wasting an excellent chance by slicing his shot wide reminded Arsenal they needed a second goal to finish off Sunderland.
They almost got it when Cazorla was narrowly off-target shortly before the departure of Jenkinson, who collected his second yellow card for a foul on Sessegnon.
Fletcher did force two good saves from Szczesny and Titus Bramble missed from six yards, but Arsenal still went closest to another goal when the luckless Walcott hit the post 15 minutes from the end.