He made two or three crucial saves at vital times to keep the Saints' nine-point cushion on Dunfermline.
Referee Charlie Richmond booked nine players in a frantic contest which could have gone either way.
St Mirren clearly came intent on protecting their advantage at the foot of the table, as they played with just Stewart Kean up front and strung five players across midfield.
It was a no-holds barred affair with both teams competing hungrily for every 50-50 ball.
In a barren first half, Jim Hamilton threatened again as he curled a 20-yard shot just a yard too high after 33 minutes but Smith was not troubled.
At the other end, Richard Brittain's free-kick was headed wide by Ian Maxwell at the far post, but the best first-half chance fell to Stevie Crawford nine minutes from the break.
Greg Ross sent over an inviting cross from the right and the striker could just not get the direction on his downwards header to find the corner of the net.
There was an angry exchange between Hamilton and John Potter shortly before the break after the Saints' defender felt the Dunfermline man had gone down too easily in the area.
Referee Richmond booked Hamilton and David van Zanten - who had also got himself involved.
Dunfermline looked the more positive after the break but were denied by Smith. He made a superb double save to keep out firstly a header from Hamilton and then the follow-up from Crawford.
Smith again came to his side's rescue nine minutes from time when he touched a deflected free-kick from Stephen Glass past his post.