By halftime, City looked to have wrapped up the league title in record time with a 2-0 lead, shredding United apart with goals from captain Vincent Kompany and Ilkay Gundogan in a six-minute span.
But Mourinho's men were completely transformed after their manager's stirring half-time team-talk.
"It's the first time we've lost two games in a row this season and now we have to recover and try again, go back to the basics and win games", said a frustrated Guardiola. "Now we've beaten Liverpool and City close".
Raheem Sterling had three other clear chances to put City ahead, but he put them wide as United continued to struggle in the first half.
Pundits and fans alike have been in unison when expressing their dismay at Pobga being utilised in a central midfield pivot, as they feel like the 25-year-old's natural game gets curbed in such a formation.
Can United catch up to City next season?
Ex-Playboy model Kendra Wilkinson files for divorce
On Friday morning, Wilkinson shared an emotional Instagram post announcing it was her " last day of marriage " to Baskett. The former glamour model had revealed that she had been through multiple stints of severe depression and suicide attempts.
Pogba, who joined United for £89 million ($125 million, 102 million euros) from Juventus in 2016, has endured a wretched season and is by no means guaranteed to be in the starting line-up on Saturday. You could see the relief after the first goal and I'm just glad to contribute'.
And as for the alleged talks between Guardiola and Raiola, Mourinho added: "If the accusation from his agent is that he wants to go to other clubs, his price has gone up". We had more ball than normally teams get against City.
"But a good manager (Jose Mourinho) maybe said in the first half "guys, we have to do something more".
Chris Smalling then got the victor to stun City, whose hopes of sealing the Premier League title against their bitter rivals were dashed. "The number of points City win it by is going to reflect how much better they've been".
David de Gea's match-defining impact: The Spain worldwide has made a string of spectacular saves for United over the course of the campaign, and this has been one of the key reasons behind their second position in the standings.
Gundogan hit a post early in the second half but United, with the blue-haired Pogba coming to the fore after a dismal opening period, finally woke up.
"I was telling before the game we need points to finish top four and to finish second, we won points probably in the most hard place to get points, in a stadium where they won practically every match in the Premier League".