The Spaniard, with Mourinho’s men struggling to break down a ten-men West Ham side, replaced Matteo Darmian at half-time.
He went on to net Man United’s opener, ghosting into the box to expertly convert Marcus Rashford‘s pull-back after 63 minutes.
Mata, speaking after the game, shed light on the instructions Mourinho gave him prior to coming on.
“Just try to score,” said Mata.
“To create something. There was some spaces in between the defenders so I just tried to stay there to create chances for my team-mates and to try to score.
“The most important thing is that with the help of everything we were able to win today and to continue this good run of results.”
Mata’s goal was, in a sense, a fitting microcosm of his overall style: undetected, almost ghost-like, yet remarkably deadly. How many times has a lose ball into the box been met with a crisp Mata strike?
His influence is simultaneously unnoticeable and fundamental, and the game against West Ham was a case in point. With the Spaniard on the pitch Man United were crisper on the ball, packed with more purpose and zeal. It was another example of the silent assassin proving to be the unlikely hero under Mourinho.