Mancini described United's final two games, against Swansea and Sunderland, as 'easy' compared with City's clashes with Newcastle and QPR.
But O'Shea says the Black Cats deserve more respect.
John O'Shea: "Believe me, the two times City have played against us this season, they knew it wasn't an easy game.
"We've taken four points off them, and it should have been six if we think about the game at their place [a 3-3 draw in which Sunderland led 3-1].
"I think he [Mancini] is starting to enjoy his psychological games but, as the gaffer said, to call the integrity of the Premier League into question is disappointing.
"He's going for the title and he's going to try certain things. But he doesn't need to do that."
City must beat QPR on Sunday to secure the title, unless United can beat QPR and somehow overturn their eight-goal deficit.