Last season, United drew 10 games at Old Trafford, often being frustrated by the kind of deep-lying defence that Leicester manager Craig Shakespeare employed but they are now a different proposition.
"The difference is the quality of our football, we're playing better today and if we hadn't won this match I wouldn't have anyone to blame," Mourinho said.
"The team is playing very well and I'm very confident. We are comfortable on the ball and dangerous on the counter- attack," he added.
With Henrikh Mkhitaryan and Juan Mata providing creativity on the wings and Romelu Lukaku a real presence in attack, United were a constant threat and this win showed they have the options from the bench as well.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
United thought they had gone ahead in the 18th minute when Juan Mata slotted home after Schmeichel parried out a Lukaku drive but the Spaniard was ruled to have been offside.
The home side had been firmly on top in the opening 45 minutes but too often turned to hopeful long-range efforts with Paul Pogba, in particular, trying his luck from distance.
Seven minutes after the restart they should have gone ahead when Leicester defender Danny Simpson was ruled to have handled in the area but Lukaku’s penalty was superbly saved by Schmeichel, whose father Peter won five league titles for United.
Sensing the game beginning to drift towards a draw Mourinho turned to his bench.
Rashford can feel himself unfortunate to have been left out for Anthony Martial, who has twice scored from the bench this season, but he responded well.
Three minutes after being sent on for Mata the 19-year-old England forward met a Henrikh Mkhitaryan corner with a side-footed finish to put United in front.
The win was secured eight minutes from time when another substitute, Jesse Lingard, played the ball in and Fellaini flicked it past Schmeichel.
"That's why need them (the substitutes), because they can change the game," Pogba said.
"Is that a game that we might not have won last season? Yes, for sure. I was a bit scared but we keep pushing this season."
(Editing by Ed Osmond)
