Thistle recorded a comfortable, if unexpected, victory against third place Dunfermline.
The visitors were first to threaten after only three minutes when Thistle keeper Kenny Arthur was able to push Brewster's 20-yard shot round the post for a corner.
However with their first attack it was Thistle who opened the scoring after only five minutes, when Gerry Britton was able to get his head onto a Martin Hardie cross and score at the back post from six yards out.
The same player should have doubled his tally four minutes later when he reacted quickest to a Scott Paterson shot that had rebounded off the base of the post, but his effort was well saved by Derek Stillie.
The Pars created further chances for Craig Brewster and Barry Nicholson, but thanks to some resolute Thistle defending these chances were restricted to speculative long range shots.
As half time approached Thistle doubled their lead when a superb Patterson pass found Alex Burns and he ran in to shoot past Stillie from 18 yards.
The Jags continued to take the game to Dunfermline in the second half and Burns further increased their lead thanks to his great solo run which culminated with the Thistle striker coolly slotting it into the far corner.
By now the Pars looked demoralised and their play showed no signs of their lofty league position and their misery was compounded in the 70th minute when second half sub Scot McLean reacted quickest to Andrius Skerla's headed clearance to volley home from eight yards.
At this stage in the game Thistle were capable of scoring every time they went forward and Hardie will be disappointed he could do no better than tamely chip the ball into Stillie's hands when through on the keeper after 76 minutes.
Dunfermline did have a couple of late chances but they found recent Scotland call up Arthur in fine form in the Thistle goal and they took what they deserved from the game, which was absolutely nothing.