The duo struck either side of the half-time interval, both excellent strikes in their own right, and they were supplemented by goals from Ryan Naderi, Djeidi Gassama and Ross McCausland.
It delivered a first competitive triumph for Derek McInnes as manager and means the Gers head into Thursday’s UEFA Europa Conference League qualifier with FK Jablonec with some much-needed momentum.
McInnes named three changes to his side from Thursday, with latest recruit, 27-year-old Penrice, signed just yesterday and going straight into the starting lineup on the left-hand side of the defence.
St. Mirren arrived at Ibrox with plenty of confidence given their vibrant start to the season, but they were short of midfielder Paul Nsio, ineligible against his parent club.
It was the visitors who threatened first against the run of play when Chris Mochrie glided forward on the left-hand side, riding a couple of Rangers challenges before the ball broke to Eseosa Sule, who flashed wide of the target.
However, the opening exchanges very much belonged to the hosts, who pieced together a lovely move involving Djeidi Gassama and Naderi, whose lay-off into the path of Vanja Dragojevic was curled wide of the post from the edge of the penalty area.
Nico Raskin then nodded over for McInnes’ side, but it proved the precursor for the opener just three minutes later.
Only ten minutes had elapsed on the clock when Gassama’s industry robbed Jayden Richardson of possession, haring through on goal where he was thwarted by Jacob Chapman.
The danger wasn’t quite dead for the away side, however, as the ball popped up into the air off the goalkeeper and Gassama’s header across the six-yard box ricocheted unsuspectingly off Naderi and into the back of the net.
It was a much-needed relief for the Gers who certainly looked in the mood from the outset.
And one quickly became two seven minutes later with a strike which will surely be in the reckoning for Goal of the Season come the end of the season.
After a free-kick delivery was cleared only as far as Daisuke Yokota, the Japanese winger headed into the path of Dragojevic, whose first touch set him up invitingly to take on a dipping effort from 30 yards out which nestled into the postage stamp and out of the reach of the diving Chapman.
A third almost arrived moments later when Gassama chopped inside and watched his curling effort cannon off the underside of the crossbar and agonisingly back out, and it spoke to Rangers’ dominance in the opening blows that it would have been the least they deserved.
Instead, the Paisley outfit reduced the arrears at the end of the opening half-hour when the home side played their way into trouble, and Mochrie pounced to lash an unstoppable effort beyond Ivor Pandur from 20 yards out.
Yokota was unfortunate that his dipping effort from distance didn’t catch Chapman unawares, with his effort proving one of his final acts as he was replaced at the interval by Findlay Curtis.
His contribution in the second period was instantaneous, helping engineer a third for the hosts to restore their two-goal advantage.
St. Mirren were caught with bodies in the Rangers half when the ball broke to the Academy graduate, and his first-time pass sent Penrice through into space. The full-back lifted his head to see Gassama breaking beyond the visiting rearguard, and with only the goalkeeper to beat, the winger slotted a lovely finish under the advancing Chapman.
Craig McLeish’s side were still reeling from the concession of a third when the fourth goal of the afternoon hit them in quick succession.
Again, Rangers were rampant in throwing bodies into the attacking third, and after Gassama’s effort was blocked high into the air, strong work from Chukwuani and Naderi kept the ball alive enough to engineer a shooting opportunity for Penrice, who swivelled and dispatched beyond Chapman from close-range.
The visitors were afforded a route back into the contest with 24 minutes remaining when Emmanuel Fernandez was guilty of scything down Sule inside the penalty area.
Killian Phillips strode forward for the Paisley side, but after being ordered to retake his spot-kick, given referee John Beaton had yet to blow his whistle, he was thwarted by a terrific low diving save by Pandur.
Such was the relentless nature of Rangers on the day that the scoring continued to the tune of a fifth and a third of the second half alone.
Penrice was at the heart of the move down the left-hand side when he did well to dig out a delivery across the penalty area. A deft flick at the far post from Lawrence Shankland agonisingly came back off the post, but on hand to slam home the rebound from a tight angle was fellow substitute Ross McCausland to cap off the scoring.
RANGERS: Pandur, Sterling (McCrorie, 83), Makhanya, Fernandez, Penrice, Raskin, Dragojevic (Neil, 62), Chukwuani, Yokota (Curtis, 45), Gassama (McCausland, 62), Naderi (Shankland, 62)
Subs not used: Kelly, Devlin, Barron, Miovski
ST. MIRREN: Chapman, Richardson, Fraser, Gogic, John, Carr, Ramos (Taylor, 59), Phillips (Fieldson, 84), Kabia (Young, 59), Mochrie (Douglas, 84), Sule (Thomas, 75)
Subs not used: Urminsky, King, Calvin, McEvoy