Zirkzee came on from the bench.
Joshua Zirkzee praised the fighting spirit that Manchester United's players showed in defeat to Tottenham in the quarter-finals of the Carabao Cup on Thursday night.
United trailed 1-0 at half-time after a goal from Dominic Solanke and seemed to implode when play resumed for the second half.
Altay Bayindir was at fault for the opening goal and Lisandro Martinez made a mistake for the second, which was scored by Dejan Kulusevski when Martinez's weak clearance fell into his path.
Solanke scored again shortly after that, but Amorim made three changes and they had an immediate impact. Zirkzee found the net and Amad scored to make it 3-2 with 20 minutes remaining, giving the travelling away fans hope another comeback could be on the cards.
But those hopes were dashed when Bayindir made another mistake, conceding directly from a corner by failing to connect with the ball as it was played into the box.
Jonny Evans scored in added time to make 4-3 but it wasn't enough to prevent United from being on the wrong side of a seven-goal thriller.
Zirkzee spoke to MUTV after the game and said: "A bit disappointed. Losing is never fun, especially when you're in a cup that you could potentially win. It's disappointing but I think we showed great spirit as well.
"We just kept fighting and I think we can be proud of ourselves for the fact that we never stopped but yeah, disappointing. I think it was good timing [to score United's first goal of the night] and it came in front of the fans.
"The goal from Amad also gave us a real boost and that's what we tried to do when we came on. We wanted to bring energy to the pitch but sadly we couldn't change it all around. We just have to keep going. We have to deliver and we'll go out on Sunday and make sure we get three points."
United will play Bournemouth at Old Trafford in the Premier League next.