The first half was as expected a nervy affair with neither side showing any composure on the ball as very few decent chances were created. Any that did come were either saved easily or fired well-wide.
Motherwell's Steven McGarry saw his shot trundle into the arms of Chris Smith in the Saints goal and, at the other end, Mark Corcoran sent a free-kick soaring over the bar.
Then, with eight minutes to go before the break, a sigh of relief passed around the home fans as their side scored their first goal against St Mirren this season.
Paul Keegan's cross into the box was headed back into the danger area by Kevin McBride for Ross McCormack to charge in and head past Smith.
Motherwell made the best possible start to the second half, when a McBride effort was knocked wide for a corner by Smith. When the kick came in Andy Millen handled in his efforts to clear for a stonewall penalty.
McCormack stepped up to ram home his second goal of the afternoon.
Saints made two changes just after the goal and they paid immediate dividends when John Sutton pulled one back. His header from Kirk Broadfoot's cross looked easy for Colin Meldrum but somehow it sneaked through his legs.
Within two minutes Saints were level with the other sub, Billy Mehmet, netting this time. A long throw wasn't dealt with and it fell for Mehmet on the edge of the box and he curled a left-foot shot high past Meldrum.
With ten minutes left news came through of an equaliser at Inverness and the visitors almost made themselves safe only for Sutton to see his effort turned onto the bar by Meldrum before his follow-up effort was blocked for a corner.
Saints grabbed a dramatic winner with six minutes left. A free-kick was only cleared to the edge of the box where Sutton was on hand to rifle a left-foot volley high past Meldrum.