Ole Gunnar Solskjaer says Manchester United are trying to find a balance to accommodate Donny van de Beek in their starting XI.
Van de Beek came on in the 76th minute and played an instrumental role in United's winner by sparking the counter-attack that was finished by Bruno Fernandes.
Solskjaer has brought Van de Beek on in all four of United's Premier League games and the 23-year-old scored on his debut against Crystal Palace and won the corner that led to the last-gasp winner at Brighton.
However, Solskjaer turned to the dropped Paul Pogba for his first change at Newcastle before Van de Beek's introduction late in the second-half.
"He'll get his game time," Solskjaer said. "He's been fantastic in the group. I think you see today and in training, he's so neat and tidy, I don't think he lost the ball once.
"It's about finding the balance in the team. We've won 4-1 today and you're asking why I didn't start one of the players. He'll have a very good impact on the team."
United recovered from going 1-0 down in the second minute to score three goals in the last 10 minutes to secure a second league win of the campaign. Their next six games are against Paris Saint-Germain, Chelsea, RB Leipzig, Arsenal, Istanbul Basaksehir and Everton and Solskjaer hopes the Newcastle win is a fillip for their form.
"It made it a lot harder for everyone," Solskjaer added of United's worrying start at St James' Park. "It was hard enough as it was with the build-up to this game and the result from last time, and then going 1-0 down after a minute-and-a-half.
"I thought the boys responded fantastically. They were patient, resilient, they trusted what the plan was and in the end we created lots of chances to grind a win."
