The Premier League champions dominated possession after a slow start at Upton Park but were guilty of missing some gilt-edged chances as they wasted the opportunity to join Manchester United at the top of the table.
Mario Balotelli, Carlos Tevez and Gareth Barry all fluffed opportunities for City although the visitors were fortunate when West Ham's Kevin Nolan had a goal harshly ruled out.
City have now conceded just two goals in their last five Premier League fixtures having conceded seven in the five before that but they are nowhere near the free-scoring machine that took the league by storm in the early days of last season.
"When you have 65 percent of possession and four incredible chances you deserve to win," Mancini, whose side remain unbeaten in the league, told reporters.
"But I am happy for the performance because we played well. I'm unhappy that we missed these chances.
"I don't think it was a fair result. Not fair at all.
The Italian added: "We conceded a lot of goals when we started the season.
"We've improved our defence but we need to start to score like last year."
It was the first time since April that City failed to score in the league, despite Mancini starting with three strikers in Balotelli, Tevez and Edin Dzeko and throwing on Sergio Aguero from the bench late on in an attempt to seal victory.
"We continue to miss a lot of chances, every game," Mancini said. "It was the same against Swansea, we missed three or four chances in the second half and the same against Ajax.
"We created the chances and we played with three strikers. We tried everything to win but sometimes the game is like this. But, if we don't score, we don't win, this is football."
