The 19-year-old completed a £19million move to Old Trafford back in June but has had to wait to pull on Uniteds shirt after sustaining a knee injury at the end of last season while at Porto.
And the Portuguese right-back could be in line for a first-team call-up after putting in an accomplished display for the Under 23s in front of Mourinho on Friday evening.
The youngster has a serious shot at breaking into Mourinhos starting XI, with United playing three different right-backs – Matteo Darmian, Ashley Young and Antonio Valencia – in their opening three matches.
Dalot showed a number of assured touches and gave Mourinho a glimpse of his crossing ability and pace from the right flank.
Angel Gomes scored the only goal of the game at Old Trafford with a strike from the edge of the box in the 37th minute.
Speaking after Uniteds 1-0 win, Dalot told the clubs official website: I always had it on my mind that I had to be calm, take it step by step, because the injury was not too bad but it required some patience and I needed that.
Now I am here and I am ready to play whenever the coach thinks I am ready.
It was nice, the atmosphere was good, I can imagine if the stadium is full and I am very happy to come back. It feels good to be back.
It was a special night, getting my first minutes after four long months and I am really happy.
It is a really special moment for me. I just want to take this opportunity to thank the amazing medical department and the coach, who has believed in me since day one.