The diminutive forward slotted into the net from close range in the 34th minute before teeing up Alan Forrest to double the home side's lead just seconds later.
It was another insipid performance from Saints, who dropped to second bottom after losing their third straight game.
By contrast, Livingston climbed up to ninth with only their second victory of the season.
There were changes in both sides as Livingston and St Johnstone went into this clash on the back off successive losses.
Craig Sibbald and Ciaron Brown dropped to the Lions bench after picking up knocks in last weekend's loss at Celtic, Scott Robinson and Alan Forrest earning promotion to the starting XI as a result.
Saints boss Callum Davidson decided to hand goalkeeper Zander Clark his first appearance of the season as one of four alterations.
Despite suggestions that he would make his debut, there was no place in the squad for new St Johnstone midfielder Craig Bryson.
There was no lack of endeavour during the early exchanges but scoring opportunities were at a premium.
Lions midfielder Jason Holt sliced a harmless volley over the bar, while it took the visitors until the 18th minute to register their first attempt on goal.
Craig Conway's free kick was kept alive by Michael O'Halloran but Stevie May swung a wild volley well over Robby McCrorie's bar.
May was presented with a better chance six minutes later following a flowing counter-attack.
Danny McNamara sent Conway scampering down the right flank and his low cross by met by May.
But the striker's first time flick at the front post was blocked by keeper Roddy McCrorie.
However, Livingston seized control of the game with two goals within 60 seconds.
O'Halloran was dispossessed from McCrorie's kick out at a Saints corner, with Nicky Devlin and Tiffoney leading the charge on the counter.
The ball was cut back for Pittman and after he failed to get a shot away, Tiffoney pounced to slot home from close range.
Livingston got possession of the ball straight from kick off to double their lead. Tiffoney teed up Forrest on the edge of the area and the winger slid a clinical strike into the far corner.
St Johnstone boss Davison brought on Callum Hendry and Liam Gordon early in the second half in a bid to get his team going.
Jason Kerr headed over from a Conway corner as the away team searched for a goal.
They went even closer in the 71st minute when substitute Hendry had an effort headed off the line by Jason Holt after Marvin Bartley carelessly gave away possession in his own box.
Saints piled on the pressure but could not break down stubborn resistance from their hosts.