The Hammers suffered a huge blow to their hopes of staying in the Barclays Premiership with a 3-0 defeat to fellow strugglers Sheffield United on Saturday.

Tonight they face a Chelsea side which cannot afford to slip up as they chase a hat-trick of Premiership crowns and an unprecedented trophy quadruple for the season.

But West Ham have an excellent record against the Premiership's leading sides this season and Curbishley said: "We've beaten Manchester United and Arsenal so why not Chelsea?

"That's how we've got to look at it. We've got to go in there and give it our best shot.

"We have got three home games out of our last five and we have got to win them. We are still alive.

"We look to the Chelsea game as the next chance to pick three points up. It is not over."

Curbishley has demanded an immediate improvement from Carlos Tevez following a disappointing performance from the Argentina international at Bramall Lane.

The fact West Ham are in touch at all in the relegation scrap is largely down to Tevez's inspirational form over the last month.

And Curbishley needs him back to his deadly best tonight.

"I spoke to Carlos. I was disappointed with his performance on Saturday, I must admit," said Curbishley.

"The way that he has been performing and the way he has attacked recently, certainly at Upton Park, has galvanised everybody.

"We did not get that at Sheffield and I need that tomorrow night.

"I like to think that there is a bit of a stage tomorrow night for some of them - he has to be one of them - and how will they respond to it?

"Whatever happens results-wise tomorrow, the performance has to change from Sheffield.

"I was disappointed with the performance at Sheffield United but that has gone. And if the players can produce some of the performances they have put in in recent weeks at Upton Park we will have a chance."

West Ham look like being without £6.5million signing Matthew Upson for the remainder of the season after his calf injury failed to respond to treatment.

Curbishley has endured dreadful luck in defence with Upson playing just 31 minutes since signing from Birmingham in January while Danny Gabbidon underwent a second groin operation last week and Calum Davenport has been struggling with a foot problem.

"It has been a disaster for everybody," said Curbishley.

"Upson has had another series of treatments and it has not responded at the moment. We are hopeful he will start training soon but we are running out of time.

"We have only got three weeks so it will be difficult."