Roberto Mancini's side have already been knocked out of the Champions League and pressure is mounting on the Italian, despite him only signing a new five-year contract last summer.
That has prompted an admission from goalkeeper Hart, whose poor positioning allowed former City winger Adam Johnson to score Sunderland's winner at the Stadium of Light with a long-range shot, that they have found it harder to defend their title than they anticipated.
"We have dominated a lot of games, but people play differently against us now," explained Hart. "We have to adjust to that and, hopefully, the second half of the season will be better for us.
"Teams are definitely playing differently when they face us, but that comes with being the champions. It's tough when you play good football and people defend against you, but that's what it's like at the top, it's tough.
"No one else needs to know what gets said (in the dressing room), it's down to us. To be leading is difficult, but chasing is even harder. Hopefully, we can do what we did last year," added Hart (above)
City are struggling to replicate the form they showed when beating United to the title on the final day of last season and United are threatening to burst clear in the title race. More worrying is that City's defeat at Sunderland might have been even more emphatic.
"We knew all along it was going to be difficult there, it always is," said Hart. "We started really well and dominated the early stages, but that's the way football is, you have to score when you're on top and we didn't this time.
"It's how football goes sometimes. It's not that we didn't try, didn't give 100pc, or haven't shown qualities. It just wasn't there and we need to turn that around quickly. We gave it everything, but couldn't break through a Sunderland wall." (© Daily Telegraph, London)