Goals either side of half-time from Callum Gallagher and Andy Murdoch were enough to see them through, despite Liam Caddis’ equaliser in between.
The win was warmly welcomed by coach Billy Kirkwood and a decent home support, who had seen Gers fall at the first hurdle last year against Dundee United.
Whether the Light Blues can repeat their achievement of reaching the final each year between 2007 and 2011 is another matter but they’re off and running for now at least.
This was the under-20 side’s first outing of the season and it went into the game minus a number of eligible players against a side which already has competitive action under its belt.
The likes of Barrie McKay, Lewis Macleod and Robbie Crawford were all on first-team duty at Berwick while players such as Kyle McAusland were out injured.
That meant the squad was made up largely by youngsters from last season’s Glasgow Cup-winning under-17 side.
Saints actually started better and had a chance to go in front through Callum McConnell but he lifted his shot from the edge of the box over the bar.
The miss was to prove costly after 17 minutes as the home team hit back and took a lead with a well-worked goal.
Gallagher opened the scoring, heading back across Perth keeper Craig Reid’s goal after a lovely clipped cross from the left by Tom Walsh.
Jamie Burrows then set about trying to get a second and his strong running took him through the heart of St Johnstone’s midfield into the penalty area.
But having won back the ball after losing it briefly, he looked on with disappointment after setting up Walsh and seeing his curler being held by Reid.
Gers might have had a penalty shortly before the break when Gallagher was upended around the 18 yard line by Chris Moffat.
But the referee ruled the foul had occurred outside the box and Matt Clarke’s resulting free kick was both poor and lacking direction.
Kirkwood’s side continued to press after the restart and powerful work by Burrows on the right flank deserved better than Gallagher’s consequent poor connection.
Burrows himself should then have done better with his low strike from 16 yards after being fed by Gregor Fotheringham but he fired straight at Reid.
Scoring then with quarter of an hour to go would surely have sealed a win for Rangers but just seconds later they were pegged back as Caddis levelled from close range.
Kirkwood threw on Dylan Dykes and Jordan Wilson for Fotheringham and Gallagher as his team began tiring.
And with 10 minutes left mixing things up a little paid off as Murdoch fired a superb rising shot into the back of the net.
The midfielder connected with the ball ever so well on the edge of the box and Reid had no chance of stopping it.
It wasn’t a great surprise to see the visitors push hard for an equaliser as time began to ebb away from them.
But they couldn’t restore parity for a second time and it is Rangers who will go into the draw for the next stage.
RANGERS: Currie; Sinnamon, Gasparotto, Pascazio, Clarke; Fotheringham (Wilson 79), Murdoch, Aird, Walsh (Stoney 86); Burrows, Gallagher (Dykes 79).
ST JOHNSTONE: Reid; Tobin, Moffat, Rodger, Steeves; Gray, McIntosh, Stewart, Caddis; Kane, McConnell (Thomson 71).