Iran Press/ Europe: The Gunners came into the game on an upswing after ending a run of three successive defeats with victory at Chelsea, while United were attempting to bounce back from a humiliating 4-0 loss at Liverpool.
And Arsenal took three crucial points as the visitors paid the price for shambolic defending and a missed penalty by Bruno Fernandes that undermined an enterprising attacking display.
Nuno Tavares put Arsenal in front after only three minutes following errors from Raphael Varane and Alex Telles, the defender turning in a simple finish after David de Gea saved Bukayo Saka's shot.
Saka added the second from the penalty spot on 32 minutes after he was fouled by Telles.
United were a real danger in attack, the returning Cristiano Ronaldo deservedly pulling a goal back before the break.
It set the scene for a United siege, only for Fernandes to waste their big chance by carelessly rolling a second-half spot-kick against the post after Tavares handled it.
Arsenal cashed in on the reprieve when Granit Xhaka sealed the win by lashing home the Gunners' third from 25 yards with 20 minutes remaining.
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