Richard Cresswell had an early effort well saved by Hammers keeper Stephen Bywater after good work from Callum Davidson on the left hand side.
Eddie Lewis broke the deadlock in the ninth minute with a 25-yard drive that flew into the top right hand corner of the net, after he was set up by Brian O'Neil.
Marlon Harewood had a shot blocked by Andy Lonergan's legs after 13 minutes before Lewis saw a deflected shot saved by Bywater.
Two Preston corners, the first by Lewis from the right and the second by Chris Sedgwick from the other side were cleared off the line in quick succession.
Cresswell had a header saved from a Lewis cross and, just before half time O'Neil took the ball forward and hit a 20-yard right foot shot which went into the bottom right-hand corner of the net.
Preston went in very happy with a two goal lead at half time, while Hammers boss Alan Pardew used the interval to bring on Nigel Reo-Coker for Luke Chadwick.
Sedgwick was booked for dissent in the 47th minute before Reo-Coker made ii 2-1 with a left-foot shot from close range from Tomas Repka's cross.
After the goal Preston had Paul McKenna and O'Neil booked for arguing with the referee.
O'Neil had a 20-yard shot saved by Bywater. Lewis struck the bar after 56 minutes and Sedgwick's saw an effort saved as Preston sought a third.
In the closing stages West Ham substitute Bobby Zamora, warming up in front of the managers, was booked by the referee for dissent.