Onuoha admitted the City game was one of the weirdest days of his life - but he says he was pleased after Bent fired home the spot kick to secure Sunderland's first victory of the season.
"Seeing players I'd played with not so long ago as the opposition was very strange," he explained to safc.com.
"Going into that game we needed three points and it just so happened that game was against Man City.
"When the penalty came along I thought 'okay, what do I want to happen?'
"The desire for three points for us - Sunderland - was there. I never want City to lose, but we needed the win and I was happy when Darren scored."