"A very positive performance, especially with the balls going forward. Creating a lot, great intensity in his game," Mourinho said after the match.
"It was no surprise that in 80 minutes he's feeling the consequences of that intensity; it's normal as it's the first match of the season for him. But he's going to get more.
"He was waiting for quite a long time, he was deserving (of his chance)... He managed on for 90 minutes and really I told him this is not the best, this is just an opportunity for you to play and to improve your level."
Second-placed United can cut down the eight-point gap with league leaders Manchester City when they host their local rivals on Sunday and Mourinho's counterpart Pep Guardiola has said key playmaker David Silva could miss the derby through injury.
Mourinho was not convinced about Silva's absence and referred to Arsenal striker Alexandre Lacazette, who played in last weekend's game despite manager Arsene Wenger saying he was injured
Mourinho called for managers to be honest about injuries.
"When we have a problem... When players are injured, they are injured. I tell you the truth," Mourinho said.
"The truth is Eric Bailly has no chance for the weekend, Phil Jones a chance, (Marouane) Fellaini a chance, Zlatan (Ibrahimovic) a big chance and (Nemanja) Matic is injured but will play for sure. (Michael) Carrick, no chance.
"No stories of Lacazette or David Silva. All the truth. Our opponents have all these issues. They have a big issue but, in the end, everybody is ready to play... We are a bit more humble."
(Reporting by Aditi Prakash in Bengaluru; editing by Sudipto Ganguly)
