It was the Czech’s first strikes for the Light Blues since he netted on his home debut against Motherwell in August, with his opening goal dripping with quality and arriving at an opportune time for the home side in the first half.
His second, meanwhile, opened up a much-needed cushion after the interval, which proved beneficial for Philippe Clement’s men who were forced to play the final nine minutes of the contest with ten men following the dismissal of Ianis Hagi.
The Gers lined up with two changes to the side from the midweek defeat to Olympique Lyonnais in the Europa League, with Nicolas Raskin and Ross McCausland replacing Tom Lawrence and Connor Barron.
There was also a return to the matchday squad for Hagi after a 14-month absence; the Ibrox crowd reserving a special cheer for the returning Romanian when the team lines were read out.
It was an unfamiliar Sunday evening setting in Govan, owing to the later kick-off time of 8pm due to road disruption from the Great Scottish Run in Glasgow earlier in the day.
And the Light Blues almost gave the Ibrox crowd something to cheer inside seven minutes when a wicked corner delivery from James Tavernier saw Cyriel Dessers rise highest and nod over from close range.
The Gers captain was at the heart of their next moment of danger – again from a dead ball situation – after his dipping free-kick ricocheted off the head of Nicky Clark and inches over Ross Sinclair’s goal.
St. Johnstone appeared perfectly content to sit off the hosts and exploit the pace of Benjamin Kimipioka in attack, although their early endeavour only yielded a wayward effort from Matthew Smith.
The home side’s most threatening moment of the first half to that point arrived on 25 minutes.
Vaclav Cerny was the architect when he fed a neat pass into the penalty area for Mohamed Diomande to swivel and strike on his left side, but a last-ditch sliding intervention from Jack Sanders denied the Ivorian a certain opener.
However, Philippe Clement’s side didn’t have to wait too long to break open the contest as, just eight minutes later, the ball nestled into the back of the net thanks to a terrific individual contribution from Cerny.
There appeared nowhere for the Czech winger to manoeuvre when Diomande fed him a pass inside, but the 26-year-old produced a sumptuous nutmeg on Smith in midfield before curling an unstoppable effort into the bottom corner.
McCausland ought to have troubled the goalkeeper more with an effort on the stroke of half-time, jinking inside but releasing a curling effort which lacked the required power.
It was domination from the hosts, although Clement’s team talk at the interval would surely have revolved around the opportunity to turn the hatful of chances into the currency of goals.
Half-time prompted a double switch from the home side as Hagi took to the Ibrox pitch for the first time since August 2023 alongside midfield reinforcement in Barron.
Indeed, the one-way nature of the contest continued as Rangers pressed for the second goal which would have made Ibrox breathe that little bit easier.
And it duly arrived just shy of the hour-mark when Cerny doubled his tally for the evening, shimmying clear inside the penalty areas before arrowing a driven effort into the bottom corner on his unfavoured right side.
The Czech winger was purring with confidence and, after combining neatly with Tavernier on the right-hand side, his pull-back in search of Hamza Igamane resulted into an effort straight down the throat of the St. Johnstone goalkeeper.
Barjami looked certain to spring the offside trap and get in on the act with 13 minutes remaining, but his dinked finish was thwarted by Sinclair before the linesman duly raised his offside flag.
Rangers were then forced to play the final nine minutes – plus additional time – with a man disadvantage when Hagi was shown a straight red card upon a VAR review for a foul on Kimpioka on the halfway line.
Nicky Clark had the ball in the net from a tight angle for St. Johnstone shortly after, but the linesman curbed any celebrations from the away corner and any hopes of a late comeback from the Perth outfit were all but extinguished.
It proved all she wrote in the contest as the sound of the full-time whistle ushered in a fourth successive domestic triumph for Rangers heading into the international break.
RANGERS: Butland, Tavernier, Propper, Souttar, Jefte, Raskin, Diomande (Barron, 45), Barjami (Sterling, 82), Cerny (Kasanwirjo, 72), McCausland (Hagi, 45), Dessers (Igamane, 58)
Subs not used: Kelly, Balogun, Fraser
ST. JOHNSTONE: Sinclair, Raymond (Keltjens, 72), Sanders, Neilson, Clark, Wright (Sidibeh, 45), Essel (Franczak, 82), Smith, Sprangler (MacPherson, 45), Kirk (Carey, 72), Kimpioka
Subs not used: Rae, Kucheriavyi, McPake, Bright