The Hammers won 2-1 at Leicester City on Monday night to leave them just two points behind the Saints going into the final game of the season.
The Londoners must beat Hull at Upton Park and hope that Coventry avoid defeat at St Marys if West Ham have any chance of going up.
"We've stayed in the race now until the very, very end, which is what we wanted and we'll have to do our job on Saturday and hope that Coventry can do a little bit at Southampton and wait and see," said Allardyce.
"If Southampton get the jitters or the nerves or Coventry play with no fear because they've got relegated now, you know, who knows. But we have to beat Hull."
Asked how Southampton will be feeling after West Ham's win over Leicester, Allardyce added: "A little bit more nervous now than they were before the game I would think.
"We've kept the pressure on them, but it's still a slim chance."
Allardyce has been in charge at Upton Park since June 2011.