Despite showing real urgency in the second-half Mourinho resisted using his bench against the Italian giants.
Eric Bailly, Andreas Pereira, Fred, Ander Herrera, Matteo Darmian and Tahith Chong were the only outfield players available to Mourinho.
"Fellaini may or may not have been in the stands – he might have been at home I didn’t see him. And the only really attacking options I had on the bench was a young 18-year-old lad whose never played in the first team before.
"And I didn't think, given the dynamic of the game, it would have been appropriate to put him on.
"You can’t expect a young kid coming on, making his debut in a game like that, to be able to give me something like scoring a goal. So basically that’s why I didn’t make any changes and just stuck with the players we had out on the pitch."
In reference to being totally outplayed by the Serie A champions in the relentless waves of attacks, the Portuguese tactician conceded Massimo Allegri's side are far superior in every aspect.
"They had [Gonzalo] Higuain, [Mario] Mandzukic, [Paulo] Dybala but they want more. They want Ronaldo. They had [Andrea] Barzagli, [Giorgio] Chiellini, [Daniele] Rugani, they are not happy, they want more," Mourinho said.
"They want Bonucci and they go for the best players in the world. So, big club with a big past but with also a big desire to have a big future.
"I don't think we gave them too much respect. Juventus was in a different level of quality, stability, experience and know-how," he added.
"Juventus are Italian champions for seven years in a row, two Champions League finals in the last four or five years and not happy with what they have. They want more."