Sir Alex Ferguson remained defiant after Manchester United's lead at the top of the Premiership was cut to just two points following defeat at West Ham.
Alan Curbishley saw his Upton Park managerial reign get off to the perfect start following a goal from skipper Nigel Reo-Coker with 15 minutes left.
Champions Chelsea had earlier beaten Everton 3-2 at Goodison Park, with a superb 40-yard winning strike from Didier Drogba.
But Ferguson maintained: 'The championship race is not going to be decided in December.
'There are a lot of important games to come and I am happy with the form of my team - they are playing well.
'We played some fantastic football but our finishing could have been better - we had some fantastic opportunities.
'We didn't deserve to lose but we have to gather ourselves and start another charge - we have got to show our mettle.
'That's the true mark of champs and we've proved it in the past.
'Two fantastic strikes won the game for them (Chelsea) out of nothing,' added Ferguson, referring to Chelsea's 3-2 win at Everton.