A double from Ross McCausland and goals from Chris McKee and Dire Mebude helped the young Gers to victory at the Hummel Training Centre.
Early in the game, the visitors had a free-kick in a dangerous position after just three minutes which was swung into the box and eventually landed at Lewis Jamieson who took a shot first time with his effort just over the target.
Shortly after, Robbie Fraser’s cross was headed over the bar by Chris McKee before McKee’s free-kick was tipped away by the St Mirren goalkeeper but only as far as Kyle McClelland who shot over the bar.
St Mirren’s Reis Webster shot across goal on 10 minutes but his effort was just wide of Grant Thackray’s post.
In a lively start to the game, Ross McCausland saw his attempt saved as he cut inside from the right to get a shot away at goal.
Kane Ritchie-Hosler had an effort on the 20th minute as he was played in by Chris McKee but his effort was tipped behind by the keeper.
As Rangers searched for an opened, the St Mirren keeper was again tested as he denied Ross McCausland from breaking the deadlock before he blocked a Harris O’Connor effort.
On the 25th minute Matt Yates cross was headed back into the centre of the penalty box by Kyle McClelland and hit first time by Chris McKee but drifted just over the bar.
David McCallum’s side continued to pressure as Matt Yates done well to win the ball back in a dangerous area before playing out wide to Ross McCausland but Chris McKee couldn’t get a touch on the cross across the face of goal to divert it goal wards.
The goal did come on the 38th minute a cross was headed towards goal by Matt Yates but was blocked before breaking for Ross McCausland who drilled a low effort beyond the keeper.
McCausland almost had a second a few minutes later as Kane Ritchie-Hosler’s corner found him in space to curl a shot towards goal but it was just over the bar.
However, the second did come on the 50th minute as Matthew Henderson’s ball towards goal bounced off the post and McCausland was on hand to finish for his second of the game.
McCausland had a chance for a hat-trick on the 58th minute as he curled an effort towards goal but it was pushed away by the keeper.
Rangers added a third on the 63rd minute as Aaron Lyall went on a good run down the left beating the defenders before finding Chris McKee in the box and the striker made no mistake in beating the keeper.
St Mirren got a goal back on the 70th minute as a free-kick was swung into the box before being headed home by Chris Johnston.
The visitors came close to adding a second as Dylan Reid touched the ball just wide at the post before up the other end Umaro Balde had a shot tipped wide by the St Mirren keeper.
Rangers got their fourth with three minutes to go as Aaron Lyall crossed the ball into the box which was tapped home by Dire Mebude.
Rangers: Thackray, McClelland (Henderson), Fraser, Balde, McKinnon, O’Connor (Strachan), McCausland, (Allan) Hampl, McKee (Mebude), Yates, Ritchie-Hosler (Lyall). Subs: McConnell.