Erik ten Hag hailed Manchester United's resilience and refusal to panic after reaching the FA Cup quarter-finals with a 3-1 comeback victory over West Ham.
United were far from their best just three days after ending a six-year trophy drought with Sunday's EFL Cup triumph over Newcastle United.
A Nayef Aguerd own goal cancelled out Said Benrahma's opener for the industrious West Ham at Old Trafford, before United battled through to the last eight on Wednesday.
Alejandro Garnacho curled past Alphonse Areola in the 90th minute and Fred added a late strike, with Ten Hag acknowledging United may have suffered from an EFL Cup hangover.
The United manager told ITV: "It was not easy, it is never easy after you win a cup and celebrate, then you have to get back to business as usual that was our task and finally we found a way to win.
"The resilience and belief they were going to win was magnificent."
Garnacho was a constant threat down the left-hand side for Ten Hag's hosts, going close twice in the first half before delivering a moment of brilliance in the dying stages.
The 18-year-old danced in from the left flank before whipping past Areola into the bottom-right corner, ending West Ham's spell of resistance after Aguerd offered United a route back into the fifth-round tie.
"You could see he was growing into the game and taking players on, he was difficult to stop and he was really a threat," Ten Hag said of Garnacho.
"It was a great goal but I think it was the total set-up for the last 30 minutes. I had a strong feeling we could win the game, you could see the belief and composure, there was never any panic."
United will next host Fulham in the competition, a clash that Ten Hag described as "difficult" against a team that "are playing really well".
Ten Hag's men will have to improve if they are to reach the semi-finals as captain Harry Maguire suggested United caused their own problems against David Moyes' visitors.
"We made it hard work for ourselves. We were poor in the first half, we have got to start better than that," the England international told ITV.
"We conceded a soft goal but it is an amazing reaction and we kept fighting and it really felt like it was coming."
Maguire joined Ten Hag in lauding Garnacho, who impressed in a rare start, with the in-form Marcus Rashford named among the substitutes amid six United changes against West Ham.
"Garnacho is very good, he is a young boy with amazing talent, he has got the world at his feet if he works and trains hard like he is at the moment," he said, before adding: "The best teams never stop believing.
"I am not saying we are one of the best teams yet, we have a lot to do but we are getting there, we are taking steps forward. We have a philosophy, we were really trying to score. It felt like the Stretford End was sucking the goal in at the end there."