Wayne Rooney's last minute goal earned United a 3-1 victory at Old Trafford on Wednesday night and a place in the final against Aston Villa at Wembley at the end of February.
"I am very sorry because I thought we played very well," the City boss told Sky Sports
"We were under pressure for only 10 minutes. For the rest of the game we played very, very well. We were unlucky.
"I am very sorry for the players because tonight they played very well.
"When we scored our goal we played well. But this is football.
"I am sorry for the supporters because I wanted to win. We had a big chance."