The English defender seemed to commit a foul on James Milner as he rushed towards goal, an infringement which was completely missed by the referee.
City Boss Pellegrini however refused to blame the loss on that one single moment, instead lamenting the numerous chances which his team should have taken during the game to score and collect the full three points.
He said: “It doesn’t matter whether it was a foul or not because the referee decides what is a foul and what isn’t – he decided it wasn’t and that’s all that counts.
“I don’t like to blame defeats on moments like that – I think we deserved to win and we also deserved to win the other games we’ve lost this season away but the fact is we didn’t and that’s what worries me.
“The Premier League is very close and there are six or seven teams trying to win the title and there are lots of games to play – we are playing well away from home but perhaps we just need a little bit more luck.”
City midfielder Milner disagreed and felt he was fouled in the build-up to the Sunderland winner.
He said. “I fell two hands on my back and he gave me a little shove which made me lose my balane.”
“The referee didn’t see it so you could say it was clever play by Bardsley and he’s got away with it and scored the goal,” he continued.
Pellegrini was stunned by the latest away defeat despite enjoying more than two-thirds of the possession.
“I really can’t believe we lost this match,” said the City boss.
“Sunderland have won the match with just one chance in the whole 90 minutes while we have several opportunities to score and maybe at least take a point but we didn’t do it - this can happen sometimes in football.
“When you fall behind you are always chasing the game and the clock is against you and it becomes more difficult as time goes on and maybe you start to rush your passes trying to find a way back into the game.