After the score finished 1-1 after normal and extra-time, the tie went to penalties.
And Villa goalkeeper Sam Proctor (above) saved twice as the hosts won 3-1 on the night.
Afterwards, Shan told Villa TV, The boys showed loads of character and resilience.
“It was a tough game. Manchester United are a very tough team, they’ve got some good players and a good style of football. We played a bit deeper at times and that takes a lot of concentration, maybe not all the time physically but mentally it’s very draining.
“The lads dug deep and you could see the amount of times they went down with cramp. A big credit to them, I think they performed at their maximum tonight.”
He added: “In preparation for every round religiously we’ve practiced penalties. There have been times as a coach when I’ve been running a bit over my session and thought about if we cut that time.
“Pete Saunders has driven that and said, ‘Come on, Jim, we need to practice.’ It’s not just been practicing for this moment, we’ve been practicing for every round. The lads have had lots of rehearsal, we’ve tried to recreate pressure scenarios and I said that to them before the penalty shootout.
“The process was there and they just had to trust the process. Sam is a big game player, he’s a big character and there were some mind games in there as well. He was outstanding.”