Defeat to Everton in their last Premier League outing left City trailing leaders Manchester United by 15 points with nine games remaining.
United have shown no signs of wilting under the pressure of wresting the English title back from their near neighbours and have won their last six league matches.
"It's over but this doesn't change anything because we should do our best from now to the end," Mancini told reporters.
"Every top team, when they can't win a title, should still try to play well and win all their games."
Mancini made the same assessment last season when City trailed United by eight points with six games to go before they rallied to snatch the title on the final day on goal difference.
"This is different (to last season)," Mancini added. "I don't know how we will finish this season, because we have Chelsea four points behind us and Tottenham five points behind.
"We have nine games left and for this reason it's important we keep working hard and well."
A seemingly crucial part of City's decline in recent weeks has been the absence of captain and defender Vincent Kompany who has been out with a calf injury since Jan. 26.
In that period, City have dropped 10 points, losing twice and drawing twice, to further cement United's lead at the top of the table.
Kompany made his return to action with Belgium in a World Cup qualifier on Tuesday, a decision that annoyed Mancini who had carefully nurtured the defender back to fitness over the last two months.
"He didn't play for us for 60 days and then he went to play for the Belgium team," Mancini said.
"I did not agree with this. I think sometimes some managers of national teams should understand the situation.
"This player plays for the club, and the club, every month, pay his salary. I don't know if he is okay or not. One week before the international break he was not fit to play for us."
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