Phil Foden scored a brace, ending a seven-game goal drought and significantly contributing to City's win.
Erling Haaland netted a goal against his former club, marking his 27th of the season and his 10th in his last six appearances at the Etihad.
Dortmund's sole goal was scored by Waldemar Anton, following a series of substitutions by their manager.
Pep Guardiola implemented tactical changes, initially using out-and-out wingers and later switching to a back five to solidify the defence, with Rayan Cherki scoring City's fourth goal.