After a typically whole-hearted display, Rooney was substituted on 82 minutes and could only watch as Everton capitulated in a frantic closing period.
It wasn't a happy afternoon back at Old Trafford for Wayne Rooney.
Everton's next league game is at home to Bournemouth, one spot below them in 19th, on Saturday.
Goals from Antonio Valencia, Henrikh Mkhitaryan, Romelu Lukaku and Anthony Martial ensured the Toffees would suffer a fourth straight defeat across all competitions, conceding 12 times in the process.
3 in Associated Press Top 25
Vanderbilt , which beat a ranked K-State team on Saturday night, is not ranked despite having three wins. Ohio State still has the best chances of any Big Ten team, despite a Week 2 loss to Oklahoma.
Mourinho and Guardiola enjoyed several tussles at the top of the league table during their respective spells at Real Madrid and Barcelona, but the Portuguese claimed that he took more interest in the results of rivals who failed to win this weekend.
It wasn't just Wayne Rooney's return (and he put in a really good shift despite his off-the-pitch issues, the least of which is the two-year ban for driving under the influence he received on Monday).
Mourinho, whose side drew 15 games last season as they finished sixth, was pleased with the "clear difference" in their style of play and the ability to push on for wins this season.
The final scoreline flattered United but it was still another disappointing result for Everton, who slipped into the bottom three.
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'City did their job, I was thinking about the others, and when I saw their results, I thought it was an opportunity we can not waste'.
Lukaku scored Manchester United's third in their 4-0 win at Old Trafford, after which he ran past the away end with his hand cupped to his ear.
The Iceland worldwide, who felt the 4-0 scoreline flattered United at the weekend, claim there are too many good players in the Everton squad for their poor run to continue and expects it to end shortly. Mourinho said: "He knows that from me there is no pressure for goal scoring, my pressure is for the tactical plan, for the organisation of the team, and he knew that I was totally happy with him so no reason to lose any confidence".
Duke and Duchess of Cambridge expecting their third child
Prince William escorts Prince George to his first day of school, just like his mom Princess Diana escorted him in 1987. Kensington Palace tweeted the news that Prince George and Princess Charlotte would be joined by a royal sibling.