"I can't drag people out of the medical room, whether they're experienced or not. The players we played [yesterday] and on the bench are the players we have.
"I don't have to be too concerned about what anyone else says — the pundits — but what is clear is the squad is the squad we've got and I believe in it.
"We were clearly the better team for 45 or even 60 minutes but we made individual errors that led to four goals from five shots. That's the harsh reality."
Mourinho spent millions to turn Chelsea into title winners during his two spells at the club and Lampard made a point of stressing that was not a luxury afforded him this off-season owing to the club's transfer embargo.
"In terms of the squad, we knew we couldn't bring players in, but I know and I believe we have got really talented young players," he said.
"So let's be clear — with the injuries we have got at the minute, and the fact we could not bring players in, this is going to be a work in progress to a degree.
"There were lots of elements I liked, but four or five elements I didn't like, which were fatal for us.
"I could not bring in players that most managers of a club like Chelsea can bring in, the players to play the way you want to play. But I'm not going to complain too much about that. I want to work with what I have."
Lampard's mood contrasted starkly with Ole Gunnar Solskjaer's delight. United rode their luck at times but Solskjaer said they got their reward for their sense of adventure going forward and insisted that would be the way of things at Old Trafford this season.
"We have found a way we want to play they have made us as coaches believe in. We took risks but that's the way here, you've got to go for it — risk and reward," the manager said.
Solskjaer praised his own debutants, Harry Maguire, Aaron Wan-Bissaka and Daniel James, who got on the scoresheet, and was pleased with the way Paul Pogba recovered from a difficult start to set up the third and fourth goals.
Pogba made a point of applauding the fans at the end and was the last to leave the pitch after an off-season in which he had sought a move to Real Madrid, and Solskjaer says he has been delighted with his midfielder's attitude.
"He's a top lad and such a pro, and when he gets on that pitch, he grows more here," Solskjaer said. "He's a World Cup winner, he's come so far in his career, and there's no point letting yourself down. He lost it a couple of times but it doesn't matter — get on the ball and play.
"Paul can do everything a midfielder can. He was asked to play that sitting role, and first half, I thought Chelsea pegged us too much back, so he had to do loads of running with [Ross] Barkley down the channels. But that pass is a fantastic pass for the third goal and the run for the fourth, I just wanted him to go all the way."
