Sanchez, who joined the club earlier in the week from Arsenal, assisted the opening two goals for Marcus Rashford and Ander Herrera as he got his first minutes for his new club.
He was heavily involved throughout and was named as the man of the match as United cashed in with late goals for Jesse Lingard and Romelu Lukaku.
Speaking afterwards Mourinho spoke of the improved atmosphere within the club and what Sanchez can bring to the squad.
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Alexis Sánchez

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"I think it's no surprise for anyone after three years in the Premier League, playing every week, so everyone knows what Alexis [Sanchez] is," Mourinho told the club's website.
"He is the kind of player you buy and you don't think about adaptation in relation to English football, so it's no surprise for us," the Portuguese manager added.
"Alexis Sanchez is a fantastic addition, everyone is happy that he comes. Good players want good players. The question is always which one is going to be left out, it is not about that for us.
"We have a fantastic group of attacking players and he is another one with more maturity and experience. His choice for the second goal is a choice that a player like Marcus Rashford is too nervous to make that kind of decision. He brings maturity and class."
He also spoke highly of their opponents, who were on top for the opening twenty minutes or so as they looked to push United high.

Manchester United manager Jose Mourinho reacts

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"These matches are difficult if the attitude is not correct. In the first half they gave us a difficult time, pressing and aggressive on the ball and on the shinpads," Mourinho said.
"I could hear Darren Way on the touchline, he knew what he was saying, they were organised.
"But in the second half we had control of the game and had more space and more quality, we killed the game."
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