A first half Dylan Moyo Bahamboula goal was enough to sink St Johnstone at the Tony Macaroni Arena.
The home winger, who had looked threatening all afternoon, netted in the 35th minute with a deflected strike from the edge of the box.
Saints struggled to mount any form of comeback and Livingston goalkeeper Shamal George was a spectator for the majority of the second half.
Nicky Clark was completely absent from the Perth team-sheet and that presented Theo Bair with a rare start from the first whistle. He was partnering Stevie May.
May certainly looked lively straight from the word go and, after just 12 seconds, sent a left-footed strike narrowly wide from a Jamie Murphy looped pass.
Then, on eight minutes, the homegrown forward was suddenly one-on-one with George after taking advantage of a short Nicky Devlin header. The goalkeeper made a smart stop.
Just moments later James Brown - not renowned for his shooting from range - unleashed a thunderbolt of a strike which cracked the underside of the crossbar and went close to dropping over the line.
It had been an end-to-end opening and Livingston too had worked into some promising positions without being able to produce the final piece of quality.
As the half hour mark approached, Cristian Montano’s cross from the left found Bahamboula but his header did not have the power or direction to trouble Remi Matthews.
Bahamboula would have better luck in the 35th minute when his effort from the edge of the box, which appeared to be heading for a comfortable save, deflected off Andy Considine and ended up in the back of the net.
Saints had fallen flat towards the end of the half and that trend continued after the break.
Murphy did have a sight of goal on the hour mark but his weak shot was never troubling George in the home net.
Up the other end, a poor Brown pass set Livingston on the counter-attack through Stephen Kelly. He eventually slipped in Jason Holt who forced Matthews into a clever save with his legs.
Max Kucheriavyi and Connor McLennan were sent on - replacing Bair and Alex Mitchell - as manager Callum Davidson searched to switch the momentum.
But soon Bahamboula would almost double Livi’s lead with a prodded effort from close-range.
Adam Montgomery and Ali Crawford, then David Wotherspoon made his big return, were next to be sent on but still Saints were unable to find a way back into the game.
McLennan did have a late chance at the back post but was unable to connect with Crawford's cross.
