Bristol City were “lucky” to beat Manchester United but the result was a “beautiful day for football”, said Red Devils manager Jose Mourinho.
Korey Smith scored an injury-time winner as the Championship side beat the Carabao Cup holders 2-1.
The Robins will face unbeaten Premier League leaders Manchester City in the two-legged semi-finals.
“A team from the lower division won. A big day for them,” Mourinho told Sky Sports.