Cyriel Dessers was on target with a cool finish in the first-half before a James Tavernier penalty doubled the lead in the second-half.
There were five changes from Sunday’s Viaplay Cup final victory over Aberdeen as manager Philippe Clement freshened up his team for this league fixture.
Kieran Dowell came in for his first start since August, with John Souttar, Ridvan, Sam Lammers and Kemar Roofe also joining the starting XI.
Rangers started at Ibrox with Jack Butland in goal and a back four of James Tavernier, Connor Goldson, John Souttar and Ridvan.
John Lundstram was in midfield alongside Dowell and Sam Lammers, while Kemar Roofe was supported in attack by Ross McCausland and Abdallah Sima.
The first chance of the match fell to Rangers and it was a good move down the right as James Tavernier found the run of Ross McCausland with the youngster whipping a delivery into the box. It was cleared by St Johnstone, but Tavernier followed up to return the ball into a dangerous area with Kemar Roofe glancing just wide of the target.
With just over 15 minutes of the match played, Kemar Roofe was forced off with an injury as Cyriel Dessers came on to replace him up front.
St Johnstone were sitting deep in the Rangers half, with Clement’s men pushing for a breakthrough as Ross McCausland fired a shot wide from distance.
The breakthrough did come with 28 minutes played at Ibrox, and it was a well-worked move from the Light Blues. Connor Goldson played in James Tavernier on the right, with the full-back whipping the ball into the box in search of Cyriel Dessers.
The striker was in a good position to get on the end of the cross and showed composure with a cool left-footed finish through the legs of Dimitar Mitov and into the back of the net for his third goal in four games.
Just minutes after the goal, Alan Muir was called to look at the VAR monitor as he flashed a yellow card towards Daillang Jaiyesimi for a lunging challenge on John Lundstram. Following review, the St Johnstone winger was shown a red card as the visitors were reduced to 10-men.
Before the break, Dessers almost had a second as he was again played in by James Tavenier but his low curling shot was just wide of the left-hand post.
In another good bit of attacking play from Rangers, McCausland and Dessers linked-up with the former playing into the path of Sam Lammers who released a powerful strike towards goal but it was gathered by Mitov.
Tavernier flashed a shot inches wide just before half-time, as Dessers goal gave Rangers the 1-0 advantage at the break at Ibrox.
Philippe Clement made one more change at half-time, as John Lundstram was replaced by Dujon Sterling in midfield.
Early in the second-half from a James Tavernier corner, Abdallah Sima had a strike at goal which was just off target as Rangers looked to extend their lead at Ibrox.
Dimitar Mitov pulled off a fantastic save with 52 minutes on the clock as he got a strong hand to a strike from Sam Lammers before coming out to deny Cyriel Dessers a rebound strike.
Rangers were really dominating as Dujon Sterling did well to win the ball back in the middle of the pitch before playing in Dessers, but his effort was blocked by Mitov, before the St Johnstone number one pulled off another great save to tip wide a Sam Lammers strike.
A double change for Rangers saw Todd Cantwell and Scott Wright introduced in place of Sam Lammers and Abdallah Sima.
Cantwell had a shot just wide from the edge of the box, before Tavernier came agonisingly close to a second goal of the match with a strike from distance.
It was relentless from Rangers as a Ridvan cross was tipped away by the keeper into the path of Tavernier but his volley crashed into the side netting.
In the 83rd minute, Rangers were awarded a penalty as Scott Wright played a perfectly weighted ball into the path of Cyriel Dessers with goalkeeper Dimitar Mitov coming off his line and fouling Dessers before he could take the shot.
Following a VAR check, the penalty was confirmed with James Tavernier stepping up to the spot to roll a low right-footed spot-kick into the back of hte net and double Rangers’ advantage.
It was the last action of the match for Tavernier as with five minutes remaining the captain was replaced by Leon King.
A late free-kick saw St Johnstone try a strike at goal but it was high of the net as Rangers secured the victory.
RANGERS: Butland, Tavernier (King, 86), Goldson, Souttar, Ridvan, Lundstram (Sterling, 46), Dowell, Lammers (Cantwell, 67), Sima (Wright, 67), McCausland, Roofe (Dessers, 16).
Subs: McCrorie, Matondo, Balogun, Barisic.
St Johnstone: Mitov, Considine, Gordon, Jaiyesimi, Kucheravyi, Olufunwa (McGowan, 71), Robinson, Smith (Costelloe, 71), Sprangler (Kane, 35), Phillips (Carey, 71), Franczak (Gallacher, 60).
Subs: May, Clark, Cooke, Richards