The winger’s second-half strike, his fifth of the season, moved the Jags level on points with third-placed Inverness Caledonain Thistle having played two games more and ended a struggling run for the Glasgow side who had gone five games without a win.
However the result could have even greater consequences for Queen of the South in tenth, still six points adrift of Dunfermline at the bottom with four games to go.
Wullie Gibson’s side lost the SPFL Trust Trophy final on Sunday and enjoyed the majority of first-half possession where Ally Roy sent an early header wide.
Ruari Paton's strike was saved before Innes Cameron fired narrowly past as the scores remained goalless at the break.
But winger Tiffoney broke the deadlock for the visitors just after the hour mark as he picked up Brian Graham's ball on the halfway line and went on a solo run to slot past goalkeeper Josh Rae for what proved to be the winner.
Meanwhile, the Doonhamers’ SPFL Trust Final opponents Raith Rovers host Morton this afternoon trying to close in on Thistle in fourth having had their own play-off hopes dented by their midweek Fife derby defeat to Dunfermline. John Hughes’ side are in Ayrshire at league leaders Kilmarnock while second-placed Arbroath face a tricky trip to in-form Hamilton as they bid to maintain their chase, with a top-two fixture less than a fortnight away. Ayr United can ease their relegation threat when Lee Bullen’s side host third-placed Inverness at Somerset Park.