Aitor Karanka insists Middlesbrough were fitter and more confident than their Premier League opponents as they knocked Manchester United out of the Capital One Cup on penalties.
Boro, who are currently fourth in the Championship, played out 120 goalless minutes at Old Trafford before winning a penalty-shoot-out 3-1 to book a last-eight home tie with Everton.
Karanka's side went out of the competition last season following an epic shoot-out away at Liverpool and the Middlesbrough boss assured his players they outperformed the 20-time English champions on their own patch this season.
"I told my players after the game that we were better than them - we were more confident on the pitch, we were fitter than them," he said.
"For that reason, I have to say how proud I am of my players. Penalties sometimes you lose - last season we lost against Liverpool after 30 penalties - and sometimes you can win.
"The main thing is the performance, and the performance against Man United, a big team, it was amazing."
Boro's win at Wolves last weekend ended a three-game run without a win and Karanka hopes the confidence taken from their cup exploits will boost them ahead of their weekend clash with Charlton.
He told Sky Sports: "My feeling is how proud I am of my players because one week ago we were losing a game in Cardiff and everybody was thinking that Middlesbrough were going in the wrong direction.
"My players have showed everybody that they are a strong team, they are strong players and good players. When they play with the spirit that we have in the changing room we can beat everybody."