The cream of Manchester fought back to restore Premier League pride in Europe after Arsenal and Chelsea's Champions League capitulations.
United came from behind to get their campaign back on track with a 2-1 Old Trafford win over German opponents Wolfsburg.
And City did likewise, overcoming Borussia Monchengladbach 2-1 in Germany.
Spaniard Juan Mata was United's hero, equalising from the penalty spot after Wolfsburg had taken an early lead and then setting up Chris Smalling's winner with a spectacular flick.
Mata was the surprise penalty-taker for United, replacing Wayne Rooney.
City's winner came from a Sergio Aguero penalty and both Manchester managers admitted fortune smiled upon them.
United's Louis Van Gaal said: "It was a lucky penalty. We created much more chances but we didn't finish it."
City's Manuel Pellegrini, boosted by a Joe Hart penalty save, accepted: "We had a little bit of luck. I don't think we deserved to lose. Maybe we didn't deserve to win, but we won."
Football Association chairman Greg Dyke has told officials that Chelsea manager Jose Mourinho committed "a failure of his personal judgement and public behaviour" in his criticism of team doctor Eva Carneiro, it can be revealed.