The defeat left them bottom of the table and led manager Charlie Christie to resign the next day, but this time around they let two points of their own slip away.
They were 1-0 up and cruising after a first-half goal from skipper Grant Munro, but Caley sat back after the break and were punished by Billie Mehmet's late equaliser.
This was a blow then to Thistle's hopes of a first ever top six finish not to mention their fading challenge for UEFA Cup spot, but the result also underlined the recent progress made by the home side, who extended a respectable run of only two defeats in their last nine outings.
Despite glorious sunshine and unusually mild conditions, both teams looked flat from the start and an early mis-hit shot from Thistle striker Dennis Wyness was typical of the poor quality on display.
A 20-yard drive from visiting midfielder Ian Black promised and home keeper Chris Smith was equal to the challenge with a fine save at full-stretch.
Smith looked less confident when he dropped Don Cowie's low free-kick and he watched relieved as it dribbled wide.
Another Smith save then denied Wyness to keep the scoresheet blank, but that soon changed as from the corner kick slack defending allowed Munro to score-left footed from ten yards.
Saints improved before half-time with Stephen McGinn offering a threat down the right side.
Striker Craig Dargo also wasted a decent opportunity with goalkeeper Michael Fraser momentarily off his line.
Goalscorer Munro was involved again at the start of the second half and, although the ball appeared to clip his arm, a penalty award would have been harsh.
But Caley were sitting deeper and deeper as they tried to protect their lead and Mehmet nearly capitalised with a close-range header.
Defender Ian Maxwell volleyed over from Mark Corcoran's free-kick and substitute Jim Hamilton saw a shot cleared off the line by Roy McBain as St Mirren kept pushing.
They were finally rewarded 15 minutes from time when Mehmet converted the rebound after Fraser's reflex save had denied Hamilton.
Inverness tried to go back to attack after defending for so long but they never really looked likely to score again and Corcoran might even have won the game for Saints with a late half-volley.