City won 2-1 thanks to Haaland, after he chose to make himself available following the passing of a close family friend during the week.
“(He told me he wanted to play) yesterday. That’s his strength. For 90 minutes you forget your personal life,” Guardiola said.
“It has been tough for his family, for anyone to pass away at that age is difficult for every human being.
“He has been down in the locker room, but we try to take care of everyone and be close to them.
“Yesterday he was much better in his mood and the best way sometimes is to do your job. He, for many years, has done it perfectly.
“That’s his strength. For 90 minutes you forget your personal life and the punch in your face life gives to you.
“If he’s not ready to play he will come to me and say he is not ready to play. He has so much quality and he is a weapon that we have to use it.
“When teams are one against one, Ederson has the long passes. For 93 minutes he forgets and just plays.”