Saints were dealt an agonising late blow when a Callum McGregor strike deep into injury-time gave Celtic the points at The SMiSA Stadium.
The Buddies created numerous chances and were dealt yet more frustration when they saw a second-half goal disallowed for the fourth home match in a row when Conor McMenamin was ruled as interfering with play when Liam Scales sent the ball into his own net.
The Northern Irishman was one of two changes from the side that lost to Hibernian prior to the international break. He came in for countryman Liam Donnelly, while Alex Gogic returned from suspension to replace Richard King.
Saints started brightly and should have taken the lead with just seven minutes on the clock. Declan John's brilliant low delivery took out the entire Celtic defence with McMenamin getting a slight touch on it, but it turned wide. Frustratingly, had the forward not touched it, Jayden Richardson would have been on hand to knock into the net at the back post.
Celtic had their first real opportunity on 15 minutes when Sebastian Tounekti cut in from the left and fired a strike inches over the bar.
McMenamin again came close to breaking the deadlock just before the half-hour mark. He picked the ball up around 25 yards from goal and set himself up for the shot. He struck it well but saw it clip the post before going wide. The Buddies passed up another big opportunity as the game edged towards the half-time interval. Mikael Mandron saw two efforts blocked before Miguel Freckleton scooped over the bar on the follow-up. With Kasper Schemeichel on the ground, any effort on target was likely to hit the net.
The visitors made a change at the break when they introduced Luke McCowan in place of Johnny Kenny. That saw Daizen Maeda move through the middle and the Japanese forward looked to cause problems after the restart. Freckleton made an important block to deny the striker early into the second-half with Gogic then making a brilliant challenge to stop him running through on goal.
Saints weathered Celtic's early pressure and thought they'd made the breakthrough on 69 minutes. Shamal George's free-kick was flicked on by Killian Phillips. Scales, under pressure from substitute Jonah Ayunga, touched the ball beyond Schmeichel only for the offside flag to be raised. VAR took a long look at it before determining that McMenamin, who was in an offside position, had interfered with play and caused Scales to knock into the net. It's the fifth goal Saints have seen disallowed in their last four home league matches.
The Buddies passed up a big chance to take a late lead on 83 minutes. Declan John played a nice one-two with Mandron and raced into the area. He had Ayunga at the far post, but elected to go alone, only managing to strike straight at Schmeichel.
It looked like the points would be shared, only for Celtic skipper McGregor to find himself in a bit of space 25 yards from goal in injury-time. He smashed goalwards and found the top corner in the fifth minute of stoppage time to see the visitors steal the points.
Full-Time: St Mirren 0-1 Celtic
St Mirren: George, Fraser (c), Gogic, Freckleton, Richardson (King 82), Phillips, McMenamin (Taylor 82), Baccus (Donnelly 90), John, Nlundulu (Ayunga 67), Mandron
Subs Not Used: Tamosevicius, Sobowale, Idowu, Dijksteel, Mooney
Celtic: Schmeichel, Ralston (Nygren 72), Scales, Trusty, Tierney (Murray 72), McGregor (c), Hatate, Engels (Donovan 85), Tounekti (Yang 67), Maeda, Kenny (McCowan 46)
Subs Not Used: Sinisalo, Balikwisha, Yamada, Bernardo
Referee: Kevin Clancy
AR1: David Roome
AR2: Ross Nelson
Fourth Official: Graham Grainger
VAR: Matthew MacDermid
Attendance: 6,840
