Brentford boss Thomas Frank called Manchester United "unbelievably lucky" to beat the Bees on Wednesday night.
Ralf Rangnick's side scored three times in the second half through Anthony Elanga, Mason Greenwood and Marcus Rashford as they shrugged off a disappointing first period, during which David de Gea was able to keep Brentford at bay.
The Spanish goalkeeper made smart stops to twice keep out Mathias Jensen as the Bees attacked well in the first period, and ultimately Frank's men only had Ivan Toney's late consolation goal to show for their efforts.
Frank was left frustrated at the result, and said he couldn't believe his side lost.
"Unbelievably proud of my team. We are the smallest club in the Premier League, Manchester United the biggest," Frank told BT Sport.
"We destroyed them in the first half, they didn't have a sniff, three huge chances and there could only have been one winner of this game. They are unbelievably lucky. I know all the stuff about taking chances. They changed the system against little Brentford.
"One of those nights, fair play to David de Gea, if we get those chances again one will go in the back of the net. Our intensity killed them, we showed that in the first half, we played the Brentford way.
"Of the three goals, the second is most disappointing and difficult to come back from. The way we smashed them in the first half was fantastic, so proud of my team."
In a separate interview with BBC Sport, he added: "A bit of quality and they went 1-0 up and after that is was bit too difficult. The boys kept running, fighting and kept going. Hugely proud especially of the first half.
"They had to step up, the way we destroyed them, they were not particularly happy with that, they were huge favourites before the game. They got a goal and changed the momentum of the game. It tells everything about the players, mentality and attitude that we out ran Man United and any other day we would win."
United boss Rangnick was asked what he said at half-time in order to spark such a comeback.
"It was not a strong conversation, but obviously we had to change a few things," he said.
"First half was not good in all aspects of the game. In the second half we were more urgent, attacking higher up the pitch and taking the right decisions in the counter attack and we scored, which is the big difference.
"Anthony Elanga followed up on the performance he showed at Villa Park. He was outstanding in the second half, put in a lot of work against the ball and then scoring the first goal.
"But I am happy for all our young players tonight - three young English goalscorers."
On De Gea, he added: "He's been doing that the last couple of weeks - brilliant saves in first half. He is one of the best keepers in the world, I would say."
