Crystal Palace continued their recent revival to boost their Premier League survival hopes and leave Arsenal struggling to maintain their run of top-four finishes under Arsene Wenger.
Palace led through Andros Townsend’s close-range finish, doubling their lead when Yohan Cabaye’s shot looped in.
Luka Milivojevic clinched victory with a firm, low penalty as Palace moved six points clear of the relegation zone.
Sixth-placed Arsenal did not manage a shot on target in a poor second half.
Some travelling Gunners fans again called for manager Wenger, who has led Arsenal to top-four finishes in each of his previous 20 seasons at the helm, to leave the club.
The Frenchman’s side are seven points adrift of fourth-placed Manchester City with eight games remaining.
Follow all the post-match reaction from Selhurst Park
Feeble Arsenal put more heat on Wenger
The manner of Arsenal’s performance – disorganised, devoid of attacking ideas and lacking fight – will increase the scrutiny on Wenger yet again.
The 67-year-old has already faced protests from some supporters urging him to leave, with more calls clearly audible – along with the barracking of his players in the latter stages – at Selhurst Park.
Wenger’s contract expires at the end of the season and the club has offered him a new two-year deal, although he is still to announce whether he intends to carry on.
Arsenal had 72% possession against Palace but that mattered for little as the hosts broke quickly on the counter-attack, exploiting space down the flanks and taking their chances clinically.
The Gunners looked defensively vulnerable whenever Palace went forward, lacking leadership without injured captain Laurent Koscielny.
And when the visitors did attack, Palace keeper Wayne Hennessey was only required to make saves from Mohamed Elneny and Alexis Sanchez.
After the break, Hennessey did not even face a shot on target as as Arsenal suffered a fourth straight away defeat for the first time under Wenger.
While Wenger has never led Arsenal to a finish outside the top four, opposite number Sam Allardyce has a proud record of not being relegated from the top flight.
On this evidence, Allardyce looks much likelier to maintain his achievement than his long-time adversary.
The former England manager, who has previously kept up Bolton, Blackburn, Newcastle and Sunderland, took a while to improve Palace’s fortunes after replacing Alan Pardew in December, but the Eagles are starting to reap the rewards of his methods when it matters.
Palace had too much pace, power and passion for a lifeless Gunners side.
Although Arsenal dominated possession in the first half, Palace had the better chances and deservedly led when Townsend drilled in Wilfried Zaha’s cross from the right.
Palace leaked goals under Pardew, but have discovered defensive resilience under Allardyce – leading to four clean sheets in their past six league games.
That run has coincided with the arrival of centre-back Mamadou Sakho, the loan signing from Liverpool who again led their backline with a determined and disciplined performance.
It laid the platform for Palace to go on and secure victory after the break.
Cabaye clipped Zaha’s pass into the top corner before Gunners keeper Emiliano Martinez clumsily brought down Townsend, allowing Luka Milivojevic to confidently tuck in his first Palace goal.
“Tactically the players were aware of what had to happen to beat Arsenal,” said Allardyce.
“Arsenal have been weak defensively – they leave the centre-backs exposed.”
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