Despite unleashing Balotelli, Carlos Tevez and Edin Dzeko in the same starting line-up for the first time, the champions could find no way through against a spirited Hammers.
Mancini did not pull any punches after the game when asked about Balotelli's miss.
"This is football," he said. "I think that a player like Balotelli, when he has a chance like today, he should score.
"Because when you are a top player, if you have a chance, you should score this - but I don't think he didn't want to score."
The Upton Park blank was the first time in seven months that City failed to register a goal in a 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."