Phil McNulty, BBC Sport Chief football writer
In a largely scrappy encounter, United celebrated what they were convinced would be victory when Alejandro Garnacho raced through to score with the score 1-1 and just two minutes of normal time left. Their joy was cut short when the Video Assistant Referee adjudged he was just offside.
Manager Erik ten Hag might have been disappointed with a point after Garnacho’s disallowed goal so it was easy to understand his emotions as he left north London empty handed for the second time this season after defeat at Tottenham.
There was some optimism offered by a brief, bustling cameo from 20-year-old striker Rasmus Hojlund, the new £72m signing using his debut to show he can offer physical presence and a focal point.
On the other side of the coin, injuries to Victor Lindelof and Lisandro Martinez saw United with Harry Maguire, previously an unwanted outcast under Ten Hag, and 35-year-old emergency signing Jonny Evans trying to keep Arsenal at bay in the closing stages. A very unlikely partnership.
This was a chastening game for United, who have stuttered so far this season, and they will need to improve before they face in-form Brighton at Old Trafford when the Premier League season resumes after the international break.