Manchester City boss Roberto Mancini bemoaned a missed chance of extending a Premier League lead over Manchester United after losing to Sunderland.
The 1-0 defeat, after Ji Dong-won's injury-time winner, means City are level with United on 45 points after they lost to Blackburn on Saturday.
Mancini said: "We missed a big opportunity because we had a chance to go three points up on United.
"We are in an unlucky moment because we keep missing these chances to score."
Micah Richards and Edin Dzeko both hit the bar for City, with Sunderland goalkeeper Simon Mignolet also making several saves from Sergio Aguero and a David Silva effort.
For the hosts, striker Nicklas Bendtner was thwarted by Joe Hart early on and Stephane Sessegnon curled a second-half shot past the post.
As his team pressed for a winner, the City boss was disappointed to be outnumbered in defence in the build-up to the goal and said his team had to recognise when to settle for a draw.
It marks the second season in a row where City have lost to a 90th-minute winner at the Stadium of Light, after Darren Bent's penalty in August 2010.
"We deserved to win this game, it's incredible, but this is football," he added.
"Last year here was the same situation, I don't know how many chances we had, and we lose the game in the end on a penalty. And [this time] apparently the goal was offside.
"A team like us, we can't concede three of four counter-attacks at the end of the game. Sometimes when you are on the pitch you need to understand that there are some games when you can't score.
"At that moment, you should understand 'OK we stay' and one point is better than nil."
Defeat for City is their second in the league this season, and means they have not won away in four games. It also marks the second consecutive game in which they have not scored after a goalless draw with West Brom on Boxing Day.
Mancini explained: "We played two teams defending with all their players in the box, but we are missing a lot of chances."
City now face Liverpool at home on Tuesday, 48 hours after playing Sunderland, and face Manchester United in the FA Cup next Sunday.
Sunderland manager Martin O'Neill said he was delighted with his side's performance.
The result earned O'Neill a third win in five league matches and he said: "It's been an incredible weekend for teams and we are delighted with three points.
"It was just a remarkable performance by the team.
"The roar for the goal was deafening, and I was delighted to hear the roar for the final whistle as well.
"It was a fantastic effort, really, really fantastic."