Bayer won 2-0 at the Etihad on Tuesday night thanks to goals from Alejandro Grimaldo and Patrik Schick.
Afterwards, a proud former Liverpool defender Quansah said afterwards: "Yeah, it's an unbelievable feeling because coming into tonight, we had a lot of senior players who were absent.
"The way the boys managed to sort of pull through – everyone sort of led tonight. And I think that's what we needed: a lot of character, a lot of determination and grit.
"They've got world-class quality, and even the players who started tonight, some are world-class players playing for their countries. It was always going to be a tough task when they (Erling Haaland, Phil Foden) come on as well. And we defended a bit deeper than I would have liked to, but I'm glad we could get the win.
"When you've got young players, there's no fear – that's exactly it. It's a massive occasion, some of the lads' biggest games tonight and playing in the Champions League, it's a chance to show yourself and prove you're at the level, and tonight we were able to show that."