Manchester United midfielder Michael Carrick admits the damaging 3-1 defeat to Everton shocked his side - but insists the champions still believe they can retain their crown.
The loss left United trailing league leaders Chelsea by four points, who took advantage of the Red Devils' slip-up by beating Wolves and giving themselves a healthy cushion.
Sir Alex Ferguson's men go into the remaining 11 games knowing they need Carlo Ancelotti's side to stumble along the way, with the two sides meeting for a crunch clash at Old Trafford in April.
Carrick knows winning that game alone will not be enough to overturn Chelsea's advantage, and he conceded the loss to Everton - on the back of a glorious UEFA Champions League win at AC Milan - came as a shock.
"We were surprised at the performance on Saturday and hugely disappointed with the way the game went," said Carrick.
"We have had some massive games in the last month and played really well over that period of time.
"That is why Saturday was such a shock. I suppose we have to look at it as a one-off. We are certainly not getting too down about things.
"We have to bounce back but the manner of our performances over the past few weeks leads us to believe we can do it again."
United have the chance to make amends for the result against West Ham on Tuesday and can reduce the gap on Chelsea to one point.
And the 28-year-old says the fight for a 13th Premier League title would not be given up easily.
He went on: "It has been a funny season with the results that have been thrown up and I certainly hope there are more slips before the end.
"It is frustrating to know we need Chelsea to slip up once or twice but we need it to be a big game when they come to Old Trafford and ensure there is a lot riding on it.
"We still believe we are in there fighting. There are a lot of points to play for so we need to keep winning and apply some pressure."
The visit of Gianfranco Zola's West Ham gives Carrick the chance to take on his former club, where he plied his trade as a youngster before a move across London to Tottenham in 2004.
But the Wallsend-born midfielder knows he will have to put sentiments to one side for the game against a club where he spent six years of his career.
"West Ham gave me my chance," he said. "They took me away from home, taught me a lot of things and guided me through.
"They gave me a chance in the first team, so I have a lot to thank them for. I still have a lot of friends there who I like to see when I go back.
"But, obviously, when we kick off it is business as usual and I am desperate to get the win."