Antonio Colak scored for the third game in a row as Rangers swept St Johnstone aside to maintain their perfect start to the league season. Malik Tillman gave the patient home side the lead in the 32nd minute with a close-range header. St Johnstone continued to make life difficult for the Light Blues until Croatia striker Colak, who had scored in previous games against Union Saint-Gilloise and Kilmarnock, drove in a second from 10 yards in the 62nd minute, with late goals by substitutes Scott Arfield and Tom Lawrence adding gloss to the scoreline. It was a third Rangers victory at Ibrox in a week with three clean sheets and will boost confidence for the first leg of their Champions League play-off at home to PSV on Tuesday. With injuries to Ryan Kent and James Sands from last Tuesday’s European game, Ben Davies made his first start and Rabbi Matondo, Ryan Jack and Scott Wright also came in against unchanged St Johnstone. Giovanni van Bronckhorst gave praise to those that stepped in. “Really pleased because we changed some players today, some we had to and some we gave more minutes, so overall it was a positive day for us,” he told BBC Scotland. There was a half-hearted appeal for a penalty early on when Colak tumbled inside the area after a challenge by Alex Mitchell. The referee, Nick Walsh, took no notice. St Johnstone suffered some disruption three minutes later when Cammy MacPherson went off injured to be replaced by the former Watford midfielder Daniel Phillips for his debut. It was one-way traffic but in the 17th minute, when a deep cross bounced off the Rangers defender Borna Barisic eight yards out, Theo Blair knocked the ball wide of a post from on the ground and a good chance was gone. Advertisement Rangers kept the visitors pinned in and when James Tavernier took a Wright pass and floated the ball over to the back post, Tillman, on loan from Bayern Munich, rose high again to head in off the bar. In the 50th minute Matondo, playing off the left, cracked the woodwork with a drive from the edge of the area and Barisic cleared the bar by inches with a free-kick from a similar distance. When St Johnstone conceded a second, it was their own fault. A hesitant Drey Wright was robbed by Matondo inside the penalty area and the ball fell to Colak who swiftly turned and drove the ball low past Matthews. Colak made way for Alfredo Morelos in a triple substitution with Wright and Tillman replaced by Arfield and Lawrence. The points were already secured and it was a case of Rangers trying to add to their tally, which Arfield did with 10 minutes remaining when he converted a Matondo cutback from 12 yards. Three minutes later, Arfield set up Lawrence for his first Rangers goal and after a comprehensive domestic display Van Bronckhorst can focus on Europe and PSV.