Goals from Mathieu Baudry and Kevin Lisbie gave Leyton Orient a fifth straight win at the expense of Preston.
Centre-back Baudry netted his second goal of the season, heading in a Dean Cox cross from eight yards, to put Orient in front just before the break.
Martin Rowlands and David Mooney then combined to set up Lisbie, who fired in left-footed past Steve Simonsen.
Akpo Sodje hit a post late on for Preston, who saw their seven-match unbeaten run come to an end.
VIEW FROM THE DRESSING ROOM
Leyton Orient manager Russell Slade told BBC London 94.9:
"It was a real battle right to the death and we claimed all the spoils.
"The players dug deep in the entire game to be honest.
"The conditions today gave it an extra messy feel.
"Preston really came at us for 15 minutes and Ryan Allsop made two fantastic saves.
"We kept defending and putting our bodies on the line and were always a threat."