Pereira was handed his full Premier League debut in the opening Premier League fixture of the new campaign, and he didn't disappoint.
He played a deep role in United's midfield three with Fred and Paul Pogba ahead of him and Mourinho was impressed with what he saw.
“I don't want to go without bringing a message about Pereira, " Mourinho explained. "He was on the bench as a right winger at Valencia and came to Old Trafford as a number 6 and played phenomenally."
Mourinho also had words of praise for left-back Shaw, who he has been quick to criticise in the past.
"The game was very complete, even if I forget the goal, of course an important goal for us, but the performance was very complete." Mourinho said.
"I think one defensive mistake and probably the linesman could help him and give a free kick against Leicester but very, very complete performance.
"He just has to keep going, the mentality was very good, the tactical discipline was very good too and he had the power to move forward and score an important goal for us."