The Premier League champions squandered a number of opportunities at Upton Park as they missed out on the chance to go top of the table.
"I think that we played well, but if we want to win we've got to score and we missed four, five, six incredible chances," Mancini told ESPN.
"I'm happy for that performance, but not the result. We deserved to win."
Saturday's point has seen City stay in third place in the standings.