Brechin competed well in the first half and on eight minutes Gerry Britton headed down for Steven Hampshire to have a shot save.
In the 11th minute Hampshire played the ball inside to Kevin Byers and his drive went just over.
On 19 minutes a Hampshire cross was just behind Darren Smith but Britton gathered the ball and drove just wide of the far post.
St Mirren threatened on 22 minutes when a Charlie Adam drive was well saved by Craig Nelson.
St Mirren opened the scoring on 24 minutes when a great cross from Hugh Murray was headed home by Sutton. Back came Brechin and two minutes later Ally Mitchell drove wide from 25 yards.
Two minutes from half time Sutton found himself in again but Nelson did well to save at his feet.
On 48 minutes a netbound shot from Britton was headed clear by Kevin McGowan.
St Mirren stretched their lead on 51 minutes when Adam crossed for Sutton to slide the ball home on the back post. On the hour mark a shot on the turn by Billy Mehmet was saved by Nelson.
Three minutes later a great turn by Britton gave him a shooting chance but his effort went inches wide.
Brechin kept battling and Hampshire had a drive saved by keeper Tony Bullock. St Mirren added a third goal three minutes from time when Sutton beat Scott Walker and fired home a low drive for his third of the game.
Brechin were denied a consolation when a shot on the turn from Chris Templeman forced a great save from Bullock.