His focus now turns to claiming derby success.
"At the start of the day, we saw this replay as a new challenge and a fresh start so you can't think about the lead in the first match and what might have been," Smalling told MUTV.
"We need to make sure that we remember this defeat next season and not let it slip again.
"It will take a couple of days to get over this because a lot of us came into it with great confidence and we felt we were going to win this game.
"At least we have a good game next Monday but we need to make sure that we rally together and win this title with aplomb."