James Forrest celebrated being named as one of Fifa's 13 young players to watch by scoring as leaders Celtic survived a tough test in Paisley.
St Mirren's Marc McAusland and Celtic's Gary Hooper both forced good saves in an even first half.
Celtic goalkeeper Fraser Forster denied Paul McGowan and new Buddies signing Dougie Imrie after the break.
But Forrest's low controlled shot after 70 minutes and Scott Brown's curler 17 minutes later won it for Celtic.
Brown set up Celtic's first goal and scored the second in Paisley
And it stretched the Glasgow side's run to 12 successive wins in the Scottish Premier League as they moved five points clear of Rangers ahead of the reigning champions' meeting with Aberdeen later in the afternoon.
Celtic manager Neil Lennon had shuffled his pack, bringing in Cha Du-ri, Ki Sung-Yueng and Forrest coming in for Adam Matthews, Emilio Izaguirre and Anthony Stokes.
But, although they started well, it was the Buddies who created the first chance after 12 minutes.
Former Celtic winger Graham Carey's corner as flicked on to the far post, where defender McAusland's half-volley from 10 yards was trapped on the line between the gangly legs of Forster.
Gary Hooper showed the confidence and eye for goal that has attracted a couple of failed bids from Southampton with an audacious attempt to catch out St Mirren goalkeeper Craig Samson.
However, his swift volley on the turn from all of 35 yards was pushed wide by the former Scotland Under-21 international.
Steven Thompson was thankful for a goal-line clearance by one of his own defenders after powering a header towards his own net as he attempted to clear a corner.
The Buddies' new signing from Hamilton, Dougie Imrie, had gone straight into Danny Lennon's side in place of the experienced Gary Teale.
And a cross from the former Clyde and Inverness forward, operating on the right despite preferring his left foot, found its way to Carey at the back post, where the winger sent a half-volley across the face of goal.
Forrest, whose progress limited Carey's chances at Celtic, at last managed to evade his markers and his near-post cross was headed across goal by Hooper.
Another Forrest cross landed on top of the crossbar, but a draw at half-time was fair on the balance of play.
St Mirren came out confidently after the break and Imrie shot straight at Forster before the goalkeeper produced a superb reaction save after Paul McGowan's flick diverted a wayward shot towards goal from 14 yards.
The frustrated Lennon hauled off Georgios Samaras and Ki after 57 minutes and the introduction of Kris Commons and Stokes gave Celtic new impetus.
St Mirren had a lucky escape moments later when Thomas Rogne's header from a corner came off McAusland's up-stretched arm.
It was the long arm of Forster that was to the fore when he superbly sent for a corner a powerful Imrie drive after the forward was found in space on the edge of the box from McGowan's neat flick.
St Mirren were undone after 70 minutes when Brown did well to play a first-time pass from Samson's punched clearance into the path of Forrest and the Scotland winger's low drive with the outside of his foot found the inside of the post from 18 yards.
Lee Mair forced another fine reaction save from Forster, while Hooper fired just wide at the other end.
However, Brown's superb finish from 18 yards ensured a victory against a Paisley outfit who have not scored in the last six meetings between the sides and who have not won a league game since beating Rangers on Christmas Eve.
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