"It was amazing. The performance and the spirit, it was amazing," reflected Boro's Head Coach.
"I am so proud of my players and our crowd should be. To beat Man United, Man City and go face to face with Liverpool and Arsenal is some achievement. Two years ago if we'd have thought we could have nights like this...
"My aim is to get the club to these kinds of stadiums every week."
After the game finished goalless with 120 exhausting minutes played, Boro progressed to a quarter-final tie at home to Everton via a dramatic penalty shoot-out where Tomas Mejias saved twice as the visitor took it 3-1 to cap an outstanding team performance.
"It was amazing game. They (Manchester United) have a lot of good players, they are very organised. But I told my players that I felt we were better than them, we were fitter and more confident. I have to say how proud how I am. The main thing is the performance and it was amazing.
"They all played well. It was a difficult team selection because I had injuries and yellow cards to consider. And we have an important game on Saturday. I have to say again how much I trust all my players because players who haven't played were amazing. Eight days ago we were almost crying after Cardiff but we've come back stronger."