Roberto Mancini was left reflecting, ruefully, on what might have been. Manchester City's manager struggled to disguise his frustration after his side wasted the chance to go clear at the top of the Premier League, surrendering to Ji Dong-won's goal four seconds from the end of stoppage time for a 1-0 defeat at the Stadium of Light.

"This is a big opportunity missed because we could have gone three points clear of Manchester United but we have to refocus now and put this defeat out of our minds," said Mancini, whose team are level on points with United, albeit with a better goal difference. "We have another important game in just two days at home to Liverpool so we have to put this out of our minds now."

City's manager refreshed his starting lineup and arguably paid the price for resting some of his best players against Martin O'Neill's injury-hit team. "We had to win this game," said Mancini, who was so upset at the end he walked up the tunnel having forgotten to shake O'Neill's hand. "A strong team can't concede this game, so this moment is a strange situation."

It was not lost on Mancini that, as Sunderland broke forward for their winner, five out-of-position City players were left standing virtually still. "I'm really disappointed. We can't concede to a counterattack like that at the end," he said. "In the first half we didn't play very well but in the second half we were much better and had a lot of chances to score. We didn't score but then we conceded two or three counterattacks in the last 10 minutes, which were really dangerous. Sometimes you can't win games because it's too difficult but you should not lose. We needed to defend those counterattacks better."

Ji's goal meant that City's 19 shots and twice striking the bar counted for nothing. "We were very unlucky," said Mancini, who thought Ji was marginally offside. "But there are days when sometimes things don't go your way and no matter how hard you try it's not going to be your day. We didn't get the offside decision on the goal and now we have to move on. I think we are having a bit of bad luck at the moment but we'll look to respond quickly against Liverpool."

It is likely he will field a different side at the Etihad Stadium. "I changed six or seven players today but we play two games in 48 hours, so it's impossible to play the same players," he said.

O'Neill, whose recalled goalkeeper Simon Mignolet played in a face mask protecting a fractured eye socket, had no choice but to deploy people out of position but was left delighted by their efforts. "It was a remarkable performance," said Sunderland's manager, close to losing his voice. "To contend with all our injuries like that was extraordinary. It was a fantastic game. We're fighting for our lives in this league and we defended with our lives. Our spirit is fantastic. I'm ecstatic."