Mourinho splashed out £75million in the summer window to bring Lukaku to Old Trafford.
The Belgian has already repaid his manager’s faith, making an explosive start in the Premier League, scoring three times for the Red Devils.
Lukaku had problems in the past with Mourinho and was sold to Everton.
Despite getting on the wrong side of Mourinho previously, Lukaku insists he feels blessed to get a chance to play for the Portuguese tactician again.
“I wanted to play for Mourinho since I was 11,” Lukaku told the BBC’s The Premier League Show.
“When you get another chance like that, you don’t say no. I’m really grateful for the second opportunity.”
And Lukaku insists he wasn’t daunted about the challenge facing him at United, adding: “You know the expectations are really high [when you play for United].
“But I was mentally prepared, I was just waiting for the opportunity to come.”
United, who travel to face Stoke tomorrow (5.30pm), have collected maximum points from their first three games.
Liverpool could go above United for a few hours at least should they overcome Manchester City in the lunchtime kick-off at the Etihad (12:30pm).