Kemar Roofe scored his first hat-trick for the Ibrox club as they repaired the gap at the top to six points after St Johnstone’s 7-0 dismantling by rivals Old Firm the day before.
Joe Aribo added a sumptuous fourth for Giovanni van Bronckhorst’s side who now face a potentially season-defining week as they attempt to overturn a 1-0 deficit in the second leg of their quarter-final the Europa League against Braga at Ibrox on Thursday before next Sunday. Scottish Cup semi-final against Celtic at Hampden.
Despite the presence of heavy Rangers support who filled the stands behind the two goals at Paisley, the mood was flat for long stretches.
From both sides’ perspective, it was hard to shake off the idea that their Premiership fates had already been determined ahead of the post-separate encounters.
St Mirren had already been relegated to a place in the last six by Saturday’s results. Their aim now is to ensure they are not dragged into the relegation equation, but their hopes of gaining anything from this contest were shaken in the opening two minutes.
Roofe’s opener was built well by Rangers, with Connor Goldson’s long ball clearing James Tavernier down the right before the captain fired a cross to Ryan Kent from across the box.
St Mirren was slow to react when Kent sent the ball back into the penalty area where Roofe had plenty of time he needed to guide a header past Dean Lyness.
Rangers failed to build any immediate momentum from that quick start and had to make a change in midfield after just 26 minutes when John Lundstram limped off to be replaced by Steven Davis.
The Saints, with former Rangers winger Jordan Jones and Wolves midfielder on loan Connor Ronan, responded with a bang without creating clear openings to equalise.
Rangers suffered another blow in the first half when Filip Helander required lengthy treatment after a clash with Eamonn Brophy and was replaced by 18-year-old Leon King.
In the added four extra minutes, Rangers doubled their lead. Aaron Ramsey should have done it when he hit the crossbar when it looked easier to score, but seconds later Roofe netted his second header of the afternoon from a classic cross from Tavern.
Thinking back to Thursday, van Bronckhorst made two more changes early in the second half as James Sands and Scott Wright replaced Ramsey and Kent.
Any lingering prospect of a Saints comeback ended when Roofe completed his hat trick in the 50th minute, forcing the ball home from close range on the second attempt after Joe Shaughnessy initially blocked an effort after a good work on the left by Fashion Sakala.
If Roofe claimed the match ball, it was Aribo who scored the best goal of the afternoon. The Nigerian struggled to find his best form in the second half of the season but recalled his quality as he collected a pass from the snitch Wright and curled a superb left-footed shot past Lyness’ right hand in the roof. fillet.