Dunfermline started with some neat passing moves and Stephen Simmons saw his low shot fumbled by Tony Bullock only to see the ball rebound off Scott Muirhead for a goal-kick.
Saints surged to the other end and Darren Young slipped to concede possession to Mark Corcoran, who was fouled. Kirk Broadfoot's free-kick was too high. Alex Burke then struck a post after Alan Reid had released Corcoran to cross for the unfortunate striker.
Corcoran and Broadfoot both just failed to connect with a Simon Lappin cross and a lunging boot denied David van Zanten connection with another Lappin delivery.
Despite all this pressure, Dorus de Vries in the Fifers' goal was not forced into making a save, easily clutching a looping Reid shot whose pace was reduced by a defender's block.
Five minutes after the break, de Vries faced a much sterner task and was equal to it, reacting sharply to thrust out a hand to keep out a near-post header from sub Billy Mehmet, after a forceful run and cross from the dashing Corcoran.
As the second half progressed, it was clear that the players were becoming more nervous, aware of the consequences of conceding a goal.
Saints lost their attacking edge and the Pars began to enjoy more territorial advantage in their hosts' half without alarming Bullock.
A final frantic push by St. Mirren roused the crowd, but no-one could force home the vital winner.