Rayners scored the only goal of the game at the Inter & Co Stadium after 36 minutes, but had two efforts ruled out just minutes earlier, for offsides and hand ball.
After the match, the Bafana Bafana striker was named Man of the Match for his performance and explained the importance of the result as Sundowns bid to reach the knockout rounds.
Rayners said on KickOff: "For me, it was about my team first, the technical team and the people that were behind us.
"For us as a team, the important thing was to get a win and that is what matters to us and I'm happy we did win the game.
"And also, we had a lot of opportunities to kill the game, so I'm happy for the victory.
"I'm happy we got a victory, and we were not surprised about them because the coach gave us all the details."
Sundowns are next in action against German giants Borussia Dortmund on Saturday.
Borussia Dortmund head coach Niko Kovac won't be expecting an easy game when his side face Mamelodi Sundowns in their second Club World Cup encounter on Saturday.
Mamelodi Sundowns striker Iqraam Rayners is hopeful his side can secure their place in the knockout rounds of the Club World Cup.
Wydad Athletic's Thembinkosi Lorch has been receiving rave reviews for his performance against Manchester City in the Club World Cup.
In Xabi Alonso's first official game in charge of Real Madrid, his side drew 1–1 against Saudi Arabian champions Al-Hilal in a tense Group H clash under searing Miami heat.
