The 25-year-old England international was a disappointed man after former club-mate Adam Johnson sneaked a long-range shot past him at the Stadium of Light to condemn City to a third successive 1-0 Barclays Premier League defeat at Sunderland.
The defeat saw the champions slip further off the pace as they attempted to reel in United, who had to come from behind three times before eventually beating the Black Cats' north-east neighbours Newcastle 4-3 at Old Trafford in stoppage time.
Blues manager Roberto Mancini was quick to point out that the season was only at the halfway stage as he assessed the implications of an unexpected defeat, and having seen his side chase down United at the back end of the last campaign to snatch the title in a dramatic finale, Hart remained equally bullish.
He told the club's official website: "We have had leads, United have had the lead - it's to-ing and fro-ing at the moment.
"We are a team of winners. It's hard and it hurts, but we have got to move on. It is hard to lead and it is hard to chase too.
"We have clawed points back before, we proved it at the end of last year. We have just got to believe."