Martial scored the only goal of the game as United recorded a 1-0 win at Old Trafford.
The France international started the match on the bench, coming on in the 70th minute for Marcus Rashford, who was forced to make way.
10 minutes later, he latched onto Romelu Lukaku’s header, to slot past Hugo Lloris.
Before he was subbed on, Martial was seen in deep conversation with Mourinho, who appeared to be giving him instructions.
“The manager told me to