St. Mirren came from behind to maintain their unbeaten record and move to the top of the table after Clyde's defeat. Two second-half goals for the home side plus a missed penalty and a last-gasp offside decision cost Thistle dearly and made for a palpitating second half.
A low-key first half burst into life in ther 17th minute when, in the visitors' first attack, Derek Fleming whipped in a free-kick from wide out on the left and Juan Escalas leapt to direct a glancing header past Craig Hinchcliffe from six yards.
Emmanuel Panther evoked memories of Kanu's goal against Chelsea when he cut past several flailing defenders and guided the ball beyond Hinchcliffe only to see Kevin McGowne head the ball off the line.
Mixu Paatelainen inspired the fight-back with impressive passing and aerial power and he drove just over after Kirk Broadfoot had headed a Hugh Murray corner against the bar.
Eleven minutes after the break, Murray's cross from the right was nodded down by the brilliant Finn, and John O'Neill took one touch before thumping a drive past Kenny Arthur.
Thistle spurned a splendid opportunity to equalise when Laurie Ellis downed Billy Gibson in the box, Fleming shooting wide of Hinchcliffe's left-hand post.
Saints went ahead after 70 minutes when another Murray cross was headed in at the far post by man-of the-match Paatelainen.
To compound Thistle's woes, Armand One's header in the dying seconds from a Kenny Milne cross was ruled out for offside.