Thistle began the game strongly with Steve Fulton going close after only three minutes. Andy Ross's cross after nine minutes found Armand One, whose header went the wrong side of the far post.
With their first and only attempt on target, Raith took a surprise lead after 10 minutes when slack Thistle defending allowed Eamon Fullerton's cross to reach Conall Murtagh, who had a simple task of tapping the ball home from six yards.
This seemed to stir Thistle and they took complete control of the half with Andy Gibson going close on 16 and 17 minutes, while One shot against David Berthelot's legs after 23 minutes.
Thistle's domination was such that they had 12 corners within the first half hour, but a combination of resolute defending and poor finishing saw all these chances come to nothing.
Thistle's equaliser came not from a corner but a throw-in when Derek Fleming found Andy Ross a full 35 yards from goal, and his snap-shot flew past everyone including Betherlot, who had no chance.
The second half continued in the same vein as the first with Thistle in complete control, and it was no surprise when they took the lead after 59 minutes Ken Milne's break forward ended in a pass to One, who side-stepped at least three Raith defenders before firing home from 16 yards.
Thistle introduced new signing Stephen McConalogue, and after 78 minutes he scored his first goal when he controlled a pass from Gibson and made no mistake from 10 yards.
The substitute then completed the rout after 85 minutes when he met a Billy Gibson clearance and his chip flew over the on-rushing keeper and into the empty net, despite the best efforts of Raith's Jonathan Smart to clear the ball.