Stevie May’s 27th goal of the season was cancelled out by Adam Rooney as the home side closed in on the runners-up spot behind Celtic, third-placed Motherwell being beaten 5-1 at Dundee United.
May, who had bagged a brace for Saints in their Scottish Cup triumph over the home side two weeks ago, capitalised on a loose pass from Clark Robertson to race clear and poke the ball past Jamie Langfield (8) for the opener.
Ryan Jack found Russell Anderson but Alan Mannus was equal to the task in the St Johnstone goal.
Another defensive error led to the equaliser with Rooney (31) latching onto a loose pass back from Frazer Wright, rounding Mannus and slotting home his ninth goal since joining on loan from Oldham in January.
There were no takers in red for a great ball played into the box from the right by Willo Flood at the start of the second half.
Johnny Hayes headed over the bar from Barry Robson’s free-kick but there was a late scare for the home fans when Langfield took an air-kick at a back pass and the ball trundled past the post.
It had been a quiet second half but there was still time for late drama with Hayes hitting the post with an acrobatic overhead kick as the Dons extended their unbeaten league run to 11 games.