Millwall stayed in the hunt for a Championship play-off place and dealt a blow to Preston's survival hopes with a thumping victory at the New Den.
The visitors held out until the 42nd minute before Darren Purse headed home James Henry's corner.
Two minutes later, the Lions doubled their lead when Josh McQuoid fired into the top left corner from 30 yards.
Nadjim Abdou then set up John Marquis to fire in a low shot from six yards, before Henry converted a penalty.
Phil Brown's Preston side have showed signs of significant improvement in recent weeks but the Lions had the first real chance when Liam Trotter's fierce 12-yard strike was tipped around a post by Iain Turner.
The visitors went close with long-range efforts from Darren Carter, before Purse broke the deadlock.
Henry sent in an inswinging corner and the defender's firm header flew into the net from six yards.
Millwall immediately grabbed their second when McQuoid collected a pass from Marquis and fired home a superb right-footed strike.
Subsitute Abdou's neat pass was then met by Marquis who rifled into the net from close range.
It got worse for Preston after Turner felled McQuoid in the box and Henry stepped up to fire his spot-kick into the top right corner and make it 4-0.
The result lifts Millwall to within two points of sixth-placed Nottingham Forest and leaves Preston five points from safety with three games remaining.