The sides could not be separated after an enthralling 120 minutes which ebbed and flowed, with both teams on top at various points but unable to find the net.
It fell then, to the oft-dreaded spot-kicks and, when Solly March missed his effort in sudden death, with the scores at 6-6, Victor Lindelof had the chance to win it for the Reds.
The Swede did just that, sparking pandemonium in the United end. Here are a dozen talking points from a great day in the capital, which sees us set up a mouthwatering final in June…
AN FA CUP FIRST
United and Brighton went into Sunday’s game knowing the identity of the side they were bidding to face in June’s final.