The Spaniard replaced Adnan Januzaj just after the hour-mark and drove home in the 67th minute to wrap up the three points for the Red Devils at Old Trafford.
“I was thinking if I come on I would try to change the game and luckily I did it,” Mata told BBC Sport.
“The manager told me I was playing on the right, I tried to make the pitch wide and come inside as well. That is what I did. The most important thing is that we won and the three points will help us to carry on this good run.
“Right now I am very happy with the goal. I have three at this moment of the season. I always try to help the team. Hopefully now in the international break we can recover our injuries.”
The victory moved United up to sixth place in the Premier League table, but still left them 13 points behind leaders Chelsea, who were 2-1 winners at Liverpool earlier in the day.
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