The Upton Park blank was the first time in seven months that City failed to register a goal in a Barclays Premier League fixture but Mancini thought his side had done enough to win the game.
"No, no. Not a fair result," he said.
"When you have 65 per cent ball possession, 22 shots - maybe less shots on goal - you deserve to win - and we missed four incredible chances to score.
"But I am happy with the performance, because we played well, I'm unhappy with the chances that we're missing.
"When you're playing well and you have a chance, and you're missing an incredible chance, you can be frustrated ... but this is football. If you don't score, you can't win - we lost two points."