The Barclays Premier League champions drew 2-2 with Liverpool at the Etihad Stadium on Sunday, their second draw in the space of five days.
That meant another two points dropped and they now trail rivals Manchester United by nine at the top of the table, four more than a week ago.
But manager Roberto Mancini was quick to insist the title race was not over and Hart maintains the players will remain confident.
The England number one said: “We have got to be. There is no point turning up otherwise. We have got to win every game and look not to drop any points. It is a good challenge for us.
“We will always be in it, but unfortunately it’s a big gap, getting too big for our liking.
“You have to move forward, and that means we have to beat Southampton next week. We are nine points behind with 13 games to go, so we need the win.”
A goal apiece from James Tomkins and Luka Milivojevic handed Crystal Palace a crucial 2-0 win over Huddersfield at the John Smith's Stadium on Saturday evening.
Manchester United bounced back from their Champions League exit as they beat Brighton 2-0 at Old Trafford on Saturday night to reach the FA Cup semi-finals.
Tottenham reached the FA Cup semi-finals after they cruised to a 3-0 victory over Swansea in their quarter-final clash at the Liberty Stadium on Saturday.
Premier League basement club West Brom squandered the lead as they suffered a 2-1 defeat to Bournemouth at the Vitality Stadium on Saturday.
Chesterfield boss Jack Lester felt his side were unlucky not to claim all three points after their 1-1 draw at Cheltenham.
New Swindon manager Phil Brown revelled in his side's victory at Cambridge in his first game in charge.