This was not the first time Pogba was substituted early by Mourinho this season, although the 25-year-old had completed the 90 minutes in United's previous four league matches.
It was City's third title in seven seasons and easily its most convincing, with Pep Guardiola's team 16 points clear and still having five games to play this season.
"City won the title because they won more points than everyone else, they were the best team".
"If I had met him when I was 20 years old, I would have improved so much", the Belgium worldwide said. "I believe in myself but I don't play".
Jay Rodriguez bundled home the victor on a scramble off a corner kick in the 73rd minute, but for long portions of the match, United looked to be the same listless side with the ball that got predecessor Louis Van Gaal sacked before Mourinho took over ahead of the 2016-17 season.
It is ironic that United came back from 2-0 down against City themselves last weekend to win 3-2 and delay City's party, only to surrender so tamely on home soil.
Manchester City have won the Premier League crown with five matches to spare, making them the joint-fastest to clinch the title.
"I won eight titles and I am not on the moon because I won against Manchester City", the former Chelsea manager added. That didn't make me feel super happy and, in my opinion, it affected some of the people that were too happy.
"The mental level, the day by day, everything must be consistent until the last day so one of the things we have to improve is consistency", he said.
In his second season in charge, Guardiola, aided by the vast financial backing of City's Abu Dhabi-based owners, has created a sublime team that helped him become the first Spanish coach to win the English top-flight title.
"I think we were deservedly punished", Mourinho told Sky Sports.
But Raheem Sterling scrambled in a 97th-minute victor, and although the England forward was sent off in the celebrations that followed, it proved to be a launchpad for a special season for both Sterling and City.