LONDON • Louis van Gaal admitted he was ready to replace Juan Mata before the midfielder clinched a 1-0 victory over Watford on Wednesday with a free kick.
On a night when United named their fourth-youngest starting XI in Premier League history at 23 years, 222 days old on average, their most senior man came up with the goods.
The Spaniard curled a superb effort from 25 metres into the top-right corner in the 83rd minute to move United level on points with fourth-placed Manchester City, who have a game in hand.
Asked if he was going to substitute the 27-year-old before his winner, van Gaal said: "Yes, that was true, because he was limping at that time. But we were in a better moment, so I didn't want to change.
"I had changed the shape, put Anthony Martial in the striker's position and we were in a better shape.
"So I didn't want to make the change again and then Mata scored the goal, so I'm very happy that I let him stay on."
His decision to play two strikers at Old Trafford almost back-fired.
Fit-again Anthony Martial was deployed up front alongside 18-year-old Marcus Rashford, who had made a dream start to his United career by scoring four goals in his opening two games. But the pair looked toothless for much of the contest.
Van Gaal conceded that his side are still struggling despite winning four in a row in all competitions.
"We are fighting and we are struggling but, in the struggle, we can play fantastic matches," he said.
"We have four wins in a row, fantastic, but we have a very small selection of players at the moment. When players are coming back, they are not fit enough. You saw how (Marcos) Rojo is struggling.
"We are still in with the possibility of being in the top four of the league and we are in the quarter-finals of the FA Cup and last 16 of the Europa League. But it also means it's a full programme."
Just how stretched United's defensive resources have been was evident by 18-year-old Tim Fosu-Mensah making his full debut.
United were second-best for much of the game but the visitors paid the price after striker Odion Ighalo missed a host of chances.
The loss was tough on Watford, and on their manager Quique Flores, who coached Mata in Real Madrid's youth set-up and at Valencia.
"We played well. We tried to get a good result, but a moment of quality decided the match," Flores said.
"It was a bad result, but we had good feelings after the match because of our performance."