Mourinho left Rooney on the bench after a series of underwhelming performances from the United captain and he wasn't missed as the Premier League champions were crushed at Old Trafford.
Juan Mata, who stepped into Rooney's number 10 role, was among the scorers, but United manager Mourinho is adamant his axed star remains an important member of the team and is not sulking about the decision to leave him out.
"Wayne Rooney is a big player for me, United and this country. He is my man, I trust him completely. He is happy," Mourinho told Sky Sports after Rooney was limited to a seven-minute substitute appearance at the end of the second half.
After United were beaten in their previous two league games, Mourinho couldn't afford his Rooney gamble to backfire and he delighted with the way his team blitzed Leicester with a four-goal first half.
"It was a very good performance and result. It is not easy against them and not easy to win in the style that we did," Mourinho said.
"Today we had intensity, movement and dynamism. To be back home and beat the champions is good. Last season we couldn't beat them and this season we have beaten them twice already.
"We have lost six points in the Premier League. We have four victories which is really important.
"Today it is about the security and the happiness of the fans, I don't know when the last time that they had such a scoreline at half time."