The challenge for Mourinho is to pass on his knowledge of how to handle the big occasions, especially the more inexperienced ones in his squad.
Rashford's "childish" decision-making at Leicester just two days before Christmas as he wasted glorious opportunities during several counter-attacks called for punishment but the Portuguese retained him against Burnley three days later, albeit with Anthony Martial unavailable through injury.
"Probably you are not expecting my answer - I'm happy with the decision", he told reporters. "I would say he was in the top five with more matches for two seasons", Mourinho said.
"In a game like this, at the highest level, it is important to keep the same principles of your game", Montella said. I remember clearly him in the meetings, in the dressing room at half-time eating every word, listening to every thing. It is just the all-round game is starting to become more clear.
"Don't take too much risk, you pass, you come around the touchline, you have the crosses, you have the set-pieces, you have the finishes from distance, 18 yards, all these things".
"Marvellous" Marcus Rashford may encounter a few more bumps in the road along his development (all players do), but ultimately his quality and work ethic will see him get to exactly where he needs to be: feared as one of the most devastating forwards in Europe.
Montella's side head to Manchester with some injury problems, particularly in defence.
Rashford will not be frustrated if his manager chooses otherwise, however, as he accepted his role under Jose Mourinho this season.
As for United's left-back issues, Mourinho sees Tottenham star Danny Rose as an ideal replacement for Luke Shaw - who could move in the opposite direction as part of a swap deal.
The first goal is obviously crucial in keeping United calm, composed and in control, and the approach ought to be measured rather than cavalier while the tie remains goalless.
The latter will also be unavailable for England over the global break, with the Portuguese saying Gareth Southgate should only select Jones if he "wants to take him for the medical department because he's injured". It's like having Ronaldo back! Many others could feel equally pleased: Ashley Young contained Salah, Eric Bailly is back, brilliant and even managed to score past David De Gea.
Rashford was phenomenal at Old Trafford.
"Long balls to Lukaku and second situations". Tomorrow, it will be the same, a Manchester United with very offensive players.
While Liverpool's players struggled to find any room for manoeuvre at Old Trafford, Juan Mata showed exactly why Mourinho chose to recall him for this fixture.