United frustrated the home side and kept the crowd quiet at the Emirates in a cagey first half but Jurrien Timber broke the deadlock from a corner after the break and William Saliba repeated the feat.
The win leaves Arsenal in third place in the Premier League, behind Chelsea on goal difference and seven points adrift of leaders Liverpool, who were held to a 3-3 draw at Newcastle.
Amorim made six changes from the team that brushed Everton aside 4-0 at the weekend, dropping in-form Amad Diallo and Marcus Rashford from his starting line-up. Gabriel was a significant absence from Arsenal's defence, joining Ben White and Riccardo Calafiori on the injury list.
Amorim travelled to London with two wins and a draw from three matches in all competitions, keenly aware that Arsenal would be his biggest test yet. The Gunners hogged possession in the opening moments and had the ball in the net in the fourth minute through Gabriel Martinelli, only for it to be ruled out for offside.
Mikel Arteta's men should have been ahead just minutes later when Thomas Partey skewed his header wide from a corner. Martinelli flashed just wide from another corner midway through the first half as Arsenal continued to look dangerous from set-pieces.
United were content to bide their time when they had the ball but they looked blunt in attack. The visitors could have gone in ahead at half-time had Diogo Dalot not steered just wide with a right-footed shot in the 43rd minute.
The two teams, both in goalscoring form, produced a combined five shots in the opening 45 minutes, with none on target.
December 4, 2024
Corner routine
The game picked up tempo at the start of the second half, with Diallo replacing Tyrell Malacia for United. Feeding off a more vocal crowd, a re-energised Arsenal put United under pressure, finally breaking the deadlock when Timber headed his first goal for the club from a Declan Rice corner.
Amorim reacted quickly, bringing on forwards Rashford and Joshua Zirkzee and handing French teenage defender Leny Yoro his United debut.
Diallo won a free-kick after fine work on the right in the 66th minute and Arsenal were grateful to goalkeeper David Raya, who pushed away a powerful Matthijs de Ligt header from Bruno Fernandes's free-kick.
Arsenal doubled their lead from a Bukayo Saka corner in the 73rd minute when Partey's shot hit Saliba and beat Andre Onana. Arsenal have scored more goals from corners - 21 - than any other side in the Premier League since the start of last season.
Onana got down well to save a Kai Havertz shot as Arsenal threatened to cut loose. United just about managed to keep them out but Amorim will know that he has a big job on his hands.
December 4, 2024