After spending time on the bench in March, Pogba scored twice in the second half to help United rally to a 3-2 win and deny City the title for the time being.
Manchester United's shock 1-0 loss at home to West Brom on Sunday means that Pep Guardiola's men, who defeated Tottenham 3-1 at Wembley the evening before, have an unassailable 16-point lead at the top of the table with just five rounds to go.
Given the way they have demolished all challengers in the league, it was apparent months ago that it was only a matter of when rather than if City would take the title. "Then the first time you lose one, you think you're never going to win another ever again", he told Sky Sports.
"So to come here and win in my first season, it's fantastic for me".
'During the week I was trying to fight that because I was feeling it.' Mourinho admitted that United didn't deserve to beat bottom club West Brom because his players were guilty of trying to be too fancy.
"It's about togetherness. We're all a family at this club, and that's how I've treated it".
Now they have four, and it comes at the expense of United... at Old Trafford.More news: Restaurants, businesses offering tax day deals as deadline approaches
A week after City surrendered a 2-0 lead to lose 3-2 to United and squander the chance to wrap up the title in flawless style against their arch-rivals, it was relegation-bound West Brom who served it up on a plate.
The Catalan, who now has won three titles in three different countries after three La Liga triumphs with Barcelona and three Bundesliga crowns with Bayern Munich, admitted his EPL title was one of his best achievements.
The Portuguese gaffer revealed what he told Pogba after the derby win: "I told Paul after the City game I don't expect him to be man of the match every week". Everything was complicated. We couldn't think fast, we couldn't play fast.
But his best moment of the match came to stop Lukaku from opening the scoring after an hour, getting down low to push Lukaku's header wide of the goal and keep his side in the match.
An anonymous showing against West Brom, though, seems to have returned him to square one.
A serial victor as a manager with Barcelona and Bayern, Guardiola ended his first year in England at City without silverware - his only failure to win a trophy since his managerial career started back in 2007.