Falkirk looked like genuine championship contenders, wrapping this victory up in the first 15 minutes as they handed Saints their fourth defeat in seven league starts.
St Johnstone looked ragged as they stumbled to yet another home defeat and lost ground on their nearest mid-table rivals Queen of the South and Ross County, who both won.
Two first half free-kicks conceded by Martyn Fotheringham inflicted fatal damage to the home side's cause.
In the ninth minute, Falkirk's Russell Latapy whipped a free-kick to David Nicholls, who shot for goal. His drive was blocked but fell to John O'Neil standing a yard from goal. The midfielder hammered the ball into the net to open the scoring.
Three minutes later Fotheringham brought Andrew Lawrie down in virtually the same spot. This time Craig McPherson fed the free-kick to Nicholls, whose shot deflected off the Saints' defensive wall to beat keeper Allan McGregor for a second time.
Saints hauled one back with substitute Mark Baxter driving the ball into the net from 18 yards less with less than 10 minutes to go.
Hopes of a Saints revival, were dashed when central defender Ian Maxwell was sent off for a second yellow card three minutes from time to effectively end the home side's chances of pulling a draw out of the hat.