United won 4-2, but not before Watford had come back from from 3-0 down to make it 3-2 with five minutes remaining. It took a fantastic individual goal from Jesse Lingard to seal the points.

Ashley Young scored twice against his former club, including a wonderful free-kick to put United 2-0 up before Anthony Martial added a third before half-time.

It would have been 4-0 at the break had Heurelho Gomes not made a point-blank save from Lingard.

Romelu Lukaku squandered another chance score the fourth in the second half before Watford's fight-back thanks to Troy Deeney's penalty and another from Abdoulaye Doucoure.

And Mourinho told BT Sport: "The second half should be five or 6-0. It was even even easier to score goals in the first half than the first but we missed the chances and this is football.

"Out of nothing a penalty and 3-1 and then the game is a different one. It was easy match comfortably and in the end, with the 3-2, the game is in a grey zone. Jesse had that fantastic initiative and killed the game.

"We scored great goals. But we missed the 4-0 in a great action at the end of the first half and in the second half we had great high pressure to recover the ball high and Lukaku had that one with an open goal and then Paul Pogba's header is also a free header.

"Lots of chances but then out of nothing it's 3-1 and then the game is different. They are full of confidence, they have nothing to lose, they have no pressure. For them, to lose 3-0 or 5-0 is exactly the same.

"So after the 3-1, they come to the game and there were a few minutes where we should be smoking cigars but we are a bit in trouble."

The result moves United to within five points of leaders Manchester City, who play Southampton at the Etihad Stadium on Wednesday. It was also a first away win in the league since September, coming at a crucial time with games against Arsenal and Manchester City to come.

The two long-range strikes were Young's first goals in the league since May 2016 and came after his shot led to Lewis Dunk's own goal in Saturday's win over Brighton.

"Ashley Young trains at free kicks and his conversion rate in training is good, so it was good he had the confidence to try it, after scoring the first goal," Mourinho added to the BBC. "I was surprised that Paul Pogba gave him permission.

"At his age, Young's playing better than ever and I couldn't be more happy with him."

The 32-year-old Young was delighted to end his Premier League goal drought.

"We started well in the first half and I think they started brightly, as well," he said. "We had to dig deep. It was fantastic in the first half. Towards the end it was getting a bit nervy but Jesse has come up with the goods and got the fourth goal.

"It's nice to get on the scoresheet. I tried to claim the goal the other day but I'll definitely to claiming those two. It was more important to get the three points. It's a tough place to come."