Rangers will be crowned Scottish Premiership champions if Celtic fail to win at Dundee United on Sunday.
Alfredo Morelos’ acute finish added to Ryan Kent’s thumping strike as two goals in two minutes made the result a formality.
Ianis Hagi netted a minute after the break as Rangers – with manager Steven Gerrard serving a one-match ban in the stands – maintained their perfect home record with a 16th win.
Rangers players and some staff rushed to one corner of the stadium at full-time to acknowledge their fans, who had flouted coronavirus lockdown restrictions by gathering outside hours before kick-off.
Defeat dented St Mirren’s top-six hopes but they have a two-point lead over St Johnstone and their fate in their own hands with one pre-split fixture left.
As a measure of how far Rangers have come since their financial implosion, eight years ago this weekend they were being turned over 2-1 at home by part-time Annan Athletic in the bottom tier.
Their trek to the pinnacle of Scottish football has been long and arduous, but that will make a first top-flight title in 10 years all the sweeter for supporters.
Flares and fireworks filled the sky as a fervent atmosphere of celebration greeted Gerrard and the players on their way into Ibrox.
The hosts then crackled with intensity from the outset with a sparkling performance that showed no hint of nerves.
St Mirren had already achieved what no other side in domestic or European competition have managed this season – a win over Rangers – but their hopes of that repeating that shock League Cup success were quickly extinguished.
Kent made the 14th-minute breakthrough when he collected a Connor Goldson pass 25 yards out, feigned a right-foot shot to bamboozle Jake Doyle-Hayes before arrowing the ball into the net with his left.
Before Jim Goodwin’s men had time to compose themselves, their deficit was doubled as Glen Kamara played in Morelos down the right-hand side of the box. The angle was tight but the Colombian striker’s finish was clinical as it kissed the far post on its way in.
St Mirren’s attempted response saw Dylan Connolly dispossess Steven Davis and bear down on goal before dragging wide.
But that was rare respite from Rangers pressure and Goldson headed inches wide after Borna Barisic had lasered a free-kick on to the centre-back’s forehead.
The third soon followed after the restart as Kent bounded down the left and his cutback found Hagi at the back post to pick his spot.
St Mirren’s main concern now was preventing further damage to their goal difference, but they almost pulled one back as substitute Jon Obika’s flick from six yards out was clawed away from the top corner by Allan McGregor.
Rangers finished strongly with their former goalkeeper Jak Alnwick sticking out a leg to slice a Kent drive over his own bar, then superbly foiling Jermain Defoe from close range.
St Mirren substitute Dylan Reid made history as he came off the bench at the death to become the Paisley club’s youngest debutant at 16 years and six days.
Man of the match – Ryan Kent
What did we learn?
This was a nerveless, ruthless display from a Rangers side who have painful experience of St Mirren’s ability to produce a shock.
From the moment Kent’s opener nestled in the net, the result was never in doubt and Gerrard’s side refused to let the emotion of the occasion affect them.
St Mirren, meanwhile, diligently kept at it to avoid a heavier defeat. A first top-six finish since 1985 is still within their grasp – victory in their remaining game, away to Hamilton Academical, will guarantee it – and would be just reward for an excellent campaign from Goodwin and his team.
What did they say?
Rangers manager Steven Gerrard: “On a really big, monumental day for the club this is probably the most important three points we have delivered.
“It puts us millimetres away from being champions. We will try and stay humble. It’s tough, because we are so close.”
St Mirren manager Jim Goodwin: “We’re not going to beat ourselves up about today. If you’d offered me one game to go pre-split to get into the top six with all we’ve had to deal with Covid, we’d have bitten your hand off.”
Rangers will be glued to the TV on Sunday hoping for a Celtic slip-up at Tannadice. That result will determine whether Rangers are already champions when they return to action in the Old Firm derby at Celtic Park on 21 March (12:00 GMT).
St Mirren play their final pre-split fixture the previous day with a trip to second-bottom Hamilton (15:00).
- 5HelanderSubstituted forBalogunat 58’minutes
- 10DavisSubstituted forArfieldat 59’minutes
- 7HagiBooked at 71minsSubstituted forWrightat 74’minutes
- 20MorelosSubstituted forDefoeat 73’minutes
- 14KentSubstituted forStewartat 81’minutes
- 4ShaughnessyBooked at 73mins
- 25ErhahonSubstituted forReidat 88’minutes
- 21ConnollySubstituted forMacPhersonat 71’minutes
- 17McGrathBooked at 59minsSubstituted forFlynnat 71’minutes
- 11DurmusSubstituted forMcAllisterat 55’minutes
- 45QuanerSubstituted forObikaat 55’minutes
- Steven McLean
Match ends, Rangers 3, St. Mirren 0.