Mourinho believes his side are now demonstrating a killer instinct they lacked last season, having averaged three goals per game so far in the Premier League - an improvement on their 1.42 goal ratio in his first campaign in charge.
Sunday will mark Rooney's first encounter against his former team mates since leaving, but Mourinho remains confident that he will receive a positive reception from United fans because of his achievements at the club.
Mourinho told Sky Sports that the decision was a no brainer, "easy" and it did not require much thinking. "I don't really understand it". "For sure I would have kept some of the players that were sold, for sure I would not buy some of the players that were bought".
Mourinho's role is still a surprise, when you consider that the Portuguese Coach had sent Lukaku off on loan in his last stint in London.
"I don't say impossible [to replace Lukaku] but that was close to impossible to get someone in who will score that amount of goals that Romelu scored for Everton".
"In the second season, you have your influence at that level".
"But you are playing against other teams whose managers are in the third or second or fourth or fifth seasons".
The striker's departure left a huge void in the squad which Everton have struggled to fill, leading to a hard start to the Premier League season with four points from four games. Signings Romelu Lukaku and Victor Lindelöf were early deals, allowing the pair a full pre-season.
"The number of appearances, the number of goals, the number of trophies - I think clearly he's one of the most important players in the history of Manchester United".