For all the recent good form of the Buddies it was the visitors who started stronger with Scott Gallacher in the home goal called into early action, but having weathered some initial turbulence Saints began forcing the issue as Gary McKenzie saw his header cleared off the line and Lewis Morgan stung the palms of United keeper, Greg Fleming.
As half time neared the teams exchanged chances: Scott McKenna of Ayr smashed against the outside of the post before Lawrence Shankland fired wide of the far post when he ought to have done better.
After the break the chances kept coming at either end with Gary Harkins denied by a smart stop from Gallacher soon after the restart. Best chance of the lot though was spurned by Shankland, who failed to hit the target from a penalty on the hour mark following a trip on Jason Naismith.
It was to be a costly miss from the on-loan Aberdeen man as minutes later Ayr punished his poor spot-kick courtesy of a well-taken finish from Paul Cairney, the midfielder seizing on a loose ball 20 yards out and drilling low past Gallacher.
Under Alex Rae’s tutelage Saints may have wilted at this stage, but there is more to them these days and following the dismissal of United’s Jamie Adams for a brutal boot at Kyle McAlister salvaged a merited point through a bullet header from substitute John Sutton.