Fellaini, another of Mourinho's introductions from the bench, then netted with eight minutes remaining to seal victory, although it looked like he was offside as he converted a shot from United's other sub, Jesse Lingard.
United's flying start - 10 goals scored and none conceded - has some talking of the leaders as title favourites and Mourinho is encouraged by their displays.
"It's not me. If I don't have them on the bench I can't make successful changes", he said. "The group is solid, very, very friendly in between games and (there's) great empathy".
"I'm really happy, not for me".
"Of course, we needed to do a bit better with the ball at times but I felt for large chunks of the game we frustrated, restricted".
In Saturday's early kick-off, Manchester City scraped a 2-1 win at Bournemouth and later Newcastle United registered their first win of the season by thrashing West Ham United 3-0.
Juan Mata's disallowed goal in the first half was followed by Schmeichel guessing correctly when Lukaku stepped up from 12 yards, but Mourinho was pleased his team kept probing and were eventually rewarded.
Asked about the 28-year-old Armenia international's form now Mourinho said: "He understands me and I understand him". We played against good teams, the best team in Europe (Real Madrid) twice.
Moving up the ladder in leaps and bounds
King nearly pulled a goal back in stoppage-time after getting on the end of Gray's cross, but De Gea was alert to deny him at point-blank range as United went into the worldwide break on a high.
"I was the first to tell my board not to feel any kind of pressure from me in that respect".
"Is [Jamie] Vardy a very unsafe player?"
Romelu Lukaku also missed a penalty for José Mourinho's men but it didn't matter in the end as the Red Devils won for the third successive game, while the Foxes will be disappointed with their performance at Old Trafford. They reached the UEFA Champions League quarterfinals, and avoided relegation after a tumultous start to the season.
"We spoke about it after the Arsenal game, we worked on it but we have to put it into action out there".
Mahrez also fizzed a unsafe ball across the face of the United goal without anyone getting a touch. He was also complaining that they had not been presented with a tough challenge in their first two games.
NYC Real Estate Executive Kills Wife, Daughter Before Himself In Westchester Home
Investigators say Steven Dym , 56, killed his wife , Loretta, and his 18-year-old daughter, Caroline , before killing himself. Police Chief Ryan remarked on the tragedy, "You have a young family, and two young children, and there's a surviving child".
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