Man United survived Arsenal's onslaught, despite being down to 10 men at the Emirates Stadium, and won 5-3 on penalties.
Bruno Fernandes opened the scoring in the 52nd minute, rifling Alejandro Garnacho's pass across the goal into the top-right corner.
In the 61st minute, Diogo Dalot received his second yellow card of the game and was dismissed, leaving United with 10 men.
Just two minutes later, Gabriel equalised for Arsenal. Martin Odegaard failed to hand the Gunners a 2-1 lead when his penalty was saved by Altay Bayindir.