Substitutes Marcus Rashford and Marouane Fellaini struck late on as United claimed a 2-0 victory on Saturday that continued their 100 per cent start to the Premier League campaign.
United racked up 22 shots in a match that also saw Romelu Lukaku have a penalty saved by Leicester goalkeeper Kasper Schmeichel, who produced an inspired performance.
Mourinho is not getting carried away by United sitting on nine points from three games, but the manager believes his players' solidity, confidence and quality is a marked improvement on what they offered last season.
"We played very well," Mourinho, whose side are yet to concede a league goal, said to BT Sport.
"The team is playing very well and I'm very confident. We are comfortable on the ball and dangerous on the counterattack.
"The result was open at 0-0 and it was obviously very difficult. The blue wall was very well organised and I always give credit to that, but we kept calm and kept control.
"After missing the penalty team remained confident and we deserved it. If I had to choose a word to describe my team it would be solid."
He added: "We can look into perspective, last season we won against Leicester at home so that doesn't make a difference, but we had too many draws at home last season.
"Nine points after three matches is nothing different for us because we did that last season.
"The difference is the quality of our football, we're playing better now and if we hadn't won this match I wouldn't have anyone to blame."
Rashford and Fellaini both scored after coming off the bench, while the other sub, Jesse Lingard, created the Belgium midfielder's goal with a run and shot from the left.
"If I don't have them on the bench I can't make successful changes," he said of the impact his substitutes have had so far this season.
"The players work hard and those who are not playing and are on the bench, or in the stands, are working hard too and waiting for the chance."