Striker Kelechi Iheanacho was on target for Manchester City as they beat United 2-1 in the English Premier League game on Saturday.
First-half goals from Kevin de Bruyne – a player Mourinho sold when he was at Chelsea to Wolfsburg, and Iheanacho sent City into a 2-0 lead in the first-half before a colossal error by Claudio Bravo gifted Zlatan Ibrahimovic a goal late in the half.
Iheanacho was however pulled off for Fernando in the 53rd minute as the second half could not produce any goal.
It was the first encounter between Guardiola and Mourinho, former El Clasico sparring partners, since 2013 and gave the former Barcelona coach an eighth win in 17 encounters with the ex-Real Madrid manager.
City’s win, their 50th in competitive derby matches, saw them end United’s perfect start to the season.
It left Guardiola’s side and Chelsea, who visit Swansea City on Sunday, as the only teams in the Premier League with 100 percent records.