Robin van Persie's stoppage-time winner ended the defending champions' 37-match unbeaten home record in the Premier League and left them six points behind Sir Alex Ferguson's side in the title race.
The result deepened the gloom around the Etihad just days after an ignominious UEFA Champions League exit at the group stage but Toure remembers last season's dramatic denouement, when his side recovered from eight points behind with only six games left.
"This makes us more determined to win it," Toure said. "We are tough men, and when things get difficult, that is when you find the tough men.
"Last year was fantastic. But we have to forget what we have done in the past.
"We have to realise that sometimes you have a bad time. When you are at the top everybody wants to take you down. We have to be strong and work harder to turn this around.
"This year will be hard but we have a fantastic squad and we have the confidence to keep going until the final day."
City had displayed United-esque powers of recovery as they cancelled out a 2-0 deficit with just minutes remaining so Van Persie's deflected winner made defeat even more galling.
"It was a dagger in the heart - unbelievable," Toure added. "We thought we would win it at 2-2, but United have great experience.
"We have to be strong mentally, and strong in every other way as well, because the Premier League is not finished yet."
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