There was to be no curse of the manager of the month award, with Steve Lomas' side extending their winning run as All Saints Day came early in Perth.
Former St Mirren striker Nigel Hasselbaink slotted in the opening goal for St Johnstone after 22 minutes.
Murray Davidson fired the second from close range shortly before the break.
Lewis Guy forced in a reply for the Buddies early in the second half, but Saints thwarted intense late pressure to record their fifth straight win.
St Mirren had arived hoping for a third successive victory of their own - and their third in a row at McDiarmid Park.
Instead, it was the Perth Saints who ended an eight-game wait for a home win in matches between the two sides, the last six having not featured a home goal.
It was to prove a tale of two returning Saints, Hasselbaink in heaven after ending the game triumphant following his return to the starting line-up and Sam Parkin suffering in the purgatory of being withdrawn at half time against his former club.
St Mirren looked like a side full of confidence from winning their 5-4 thriller with Ross County last weekend as they took the game to their hosts early on.
Fit-again Kenny McLean looked elegant on his return to the starting line-up and sent a cross-cum-shot flashing across the face of goal and another drive just over.
However, St Johnstone worked their way into the game and Gregory Tade and Chris Millar both had efforts blocked in front of goal.
The first-half tide had truly turned after a strong run from Dave Mackay and, when Davidson played Hasselbaink through, the diminutive Dutchman stroked the ball past goalkeeper Craig Samson.
St Mirren's best opportunity of the opening 45 minutes was handed to them via Alan Mannus' proverbial plate, but the goalkeeper redeemed himself for his poor clearance straight to Graham Carey by beating away the winger's powerful drive with his chest.
Samson was not so lucky when he palmed away a low Gary Miller drive and it fell for Davidson to steer in the second for the home side.
The evergreen Steven Thompson was providing what few threats there were from the visitors and it was no surprise when the anonymous Parkin was withdrawn at half time.
That change had an almost immediate impact and, when Paul Dummett's low cross was touched on by Thompson, Guy was on hand to drive home from close range.
Half-time substitute Dougie Imrie, who had been replaced by Parkin in the starting line-up, was making a big impression and his low drive was turned wide for a corner by Mannus.
Lomas had complained before kick off of having only 13 fit first-team players and those who remained were beginning to run out of steam as the Buddies pressed.
However, despite a couple of penalty claims and hectic goalmouth scrambles, the visitors were unable to make their pressure tell and it was the Perth Saints who marched on to leapfrog the visitors in the Scottish Premier League table.