The 21-year-old has started the last two matches on the bench but was handed a start against Watford.
And he rewarded Mourinho's faith with a goal and assist to lead the home side to victory.
After the match, the United manager said the France ace is working silently but hard.
Manchester United boss Jose Mourinho
Anthony Martial starts for Man United against Watford, and Twitter loves it
Sat, February 11, 2017
Anthony Martial is named in Manchester United's starting XI to face Watford, and fans are delighted
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Manchester United fans are delighted to see Anthony Martial in the starting XI
He said: "Martial deserves the chance. He has worked harder than ever in the last two weeks in the way I like – silence but hard."
Mourinho also praised his team for a 'fabulous' first half performance.
He added: "In the first half the football was fabulous. The fans got behind the team just before we scored the goal because we were phenomenal.
"When I got the job they were saying at Manchester United you need to play the football in a certain way and I agree. You cannot play a counterattacking style, but then you have to analyse the situation."