Chris Kane showed his worth to Tommy Wright’s side after returning from a loan spell at Queen of the South by hitting a hat-trick while youngster Kyle McClean, pictured, marked his debut with a goal.
The Perth side got off to the quick-fire start craved on treacherous nights at unfamiliar surroundings on a dead pitch with a goal in only three minutes.
The simplicity of it will have annoyed home manager Brian Kerr as Joe Shaughnessy launched a long throw from the right that Denny Johnstone headed on and Kane cracked the ball past goalkeeper Kieran Wright.
Despite going behind so early, the hosts, who were missing 24-goal Alan Trouten due to suspension, refused to buckle.
They carved out a chance on 21 minutes when Connor Shields twisted and turned at the edge of the box. However, his parting drive was easily smothered by Alan Mannus.
There was more irritation for the visitors to deal with 14 minutes later when Ross Davidson let fly from 30 yards and Mannus had to stretch high to save.
Just before the break another lengthy hurl by Shaughnessy caused problems in the home defence as Blair Alston flicked it on. However, this time Kane fired over from eight yards out.
The Saints almost got the second half off to a lightning start as well when Jason Kerr tried his luck with a spectacular overhead kick, but the ball bounced into the waiting arms of Wright.
The second goal was only delayed until seven minutes after the interval with Kane turning provider this time with a low cross from the right that was poked home by 19-year-old McClean from six yards out.
That goal knocked the stuffing out of the Rovers and on 56 minutes St Johnstone were out of sight as Liam Craig burst through on the left and picked out Kane with a driven cross that the striker headed into the net.
Kane ensured that he would be taking the match ball home when he was on to a sliced clearance that went over the home defence in a flash before lashing past Wright.