Smalling knew how important a win tonight would be after the criticism his side have received and was delighted with their response.
"It was a massive turnaround [from the weekend], especially with players who haven't played a lot of games this season. The noise from the fans was amazing," the club's official Twitter feed quotes him as saying.
"There was a lot of doubt after the weekend so we had to go out and get a performance and we did.
"It felt like it was end to end for pretty much 90 minutes. A real cup tie."
Manchester United host West Bromwich Albion in the Premier League on Saturday.