A Sergio Aguero strike secured a 2-2 draw at home to Liverpool for City 12 minutes from time after Daniel Sturridge, against his former club, and Steven Gerrard, had turned things around after Edin Dzeko's opener.
However, the result saw United go nine points clear at the top of the table, a tally which Mancini insists can still be clawed back.
When asked if the league had been decided, the Italian responded: "Absolutely not. Two years ago Chelsea were nine points behind and when they went to play at Old Trafford two games from the end they were only two points behind.
"I don't think this is finished, but we probably now have to win all our games."
Meanwhile, West Brom head coach Steve Clarke slammed defender Goran Popov following his sending-off for spitting against Tottenham.
Clarke confirmed disciplinary action will be taken against the Macedonian, adding that his dismissal played a large part in Albion's 1-0 defeat at The Hawthorns.