Sundowns will still be smarting from their exit at the hands of Angolan side Wiliete in the CAF Champions League, and the best way to remedy that disappointment is to win more silverware.
The Brazilians were beaten finalists in the competition in 2024/25, losing to Magesi FC in the decider, while in the other two seasons since its return to the calendar they have exited in the first round.
Sundowns took the lead in the 68th minute, and the goal was made in Stellenbosch.
Antonio van Wyk picked up the ball on the left wing and cut inside before delivering a curling cross into the centre of the penalty area.
Rayners showed excellent skill to twist and steer his header goalwards, leaving Golden Arrows goalkeeper Dumsani Msibi with no chance.
Msibi had earlier produced a stunning save to deny Rayners from a tight angle, showing brilliant reflexes.
The goal was the 46th Rayners has scored for Sundowns in 94 appearances since his move from Stellenbosch at the start of the 2024/25 season, with his return of almost a goal every other game an impressive one.
The remarkable run of consecutive appearances by Tashreeq Matthews in a Sundowns shirt came to an end on Tuesday when he was left out of the matchday squad. He had featured in 81 successive games for the Brazilians before this match.
Golden Arrows' woes in front of goal continued as they never really looked like scoring, with several attempts sailing harmlessly wide.
Sundowns will have had one eye on Sunday's CAF Super Cup fixture in Pretoria against Algeria's USM Alger, another opportunity to claim silverware after winning the MTN8 and the Africa-Asia-Pacific Cup in the FIFA Intercontinental Cup.