Scott McTominay gave a sloppy first half the goal it needed, not the one it deserved.
Arsenal and Manchester United were engaged in a bit of snoozer when the Scottish national team midfielder wound up with a cut back five yards outside the 18.
[ STREAM: Man Utd-Arsenal ]
McTominay froze Leno with a clinical strike, relegating the goalkeeper to interested onlooker status as the ball sailed into the upper reaches of the goal.
The goal is McTominay’s third in Premier League play, and first of the season.
A win for the hosts would push the Old Trafford set past Arsenal on goal difference, as both teams would land on 11 points after seven matches.