Yaya Toure has insisted the Premier League title race is not over after Manchester City's derby defeat to Manchester United left them six points behind the league leaders.
The Ivorian midfielder described Robin van Persie's injury-time winner as "a dagger in the heart" but urged his team-mates to show the spirit of champions and retain their crown.
Toure scored City's first goal as they came from 2-0 down to draw level before Van Persie condemned City to a loss that the former Barcelona player said only increases their determination.
"The title race is not finished - anything but," he told City's official website "We will continue to give United problems in the league and at the end of the season I hope we will win it again. We thought we would win the game when we made it 2-2, but United have great experience and Wayne Rooney was fantastic for them.
"It was a dagger in the heart to concede a third so late in the game, but it was a fantastic game for the fans, and that is why I like the Premier League so much. It is the toughest league in the world.
"Disappointing though this defeat is, it only makes us more determined to win the title. We have to be strong mentally and strong in every other way as well, but our championship challenge is not finished."
City were eight points behind United with six games to go last season and recovered to overhaul their neighbours but Toure has warned them this season could be even more difficult.
He added: "We have to forget what we have done in the past. This year will be tough, but we have a fantastic squad and we have the confidence to keep going until the final day. We will never give up.
"We need to improve by working even harder, because when you are at the top everybody wants to take you down.
"Last year was fantastic, but we have to realise that sometimes you go through tough periods - we can turn this around. When the chips are down, that's when the tough really get going and we will show why we are champions."