Sibiya decided the last-16 tie with a low shot past goalkeeper Kennedy Mweene in the 66th minute after bypassing Motjeka Madisha with intelligent skill and movement at Lucas Moripe Stadium.
The 21-year-old, who scored his first PSL goal last term against Orlando Pirates in April, has netted three times in all competitions this season.
'Chaka', a key feature of Arrows' MDC triumph in 2015/16, is aware his fine strike has garnered attention, but insists he will maintain his focus under coach Clinton Larsen.
"I just need to remain down to earth and focused because I see this goal has sent tongues wagging. But what I need to show is commitment at training," Sibiya tells snl24.com/kickoff.
"I have to also listen to the coach's instructions and play as a team and not individually. Because all what I'm doing, I can't do it without my teammates.
"On the goal side, I never expected I would score the way I did because mainly I thought I would score from the free-kick because we've been practising them the most at training.
"But I just saw the opportunity and I felt Sundowns at the time were tired. And I used my skills and mind by ensuring I'm removing the person [Madisha] in front of me.
"As you saw it was like I was touching the ball but I was not touching the ball and I knew I'll meet it ahead.
"One-on-ones we usually do at training and I shoot with left, right and I took my time because, if any of the Sundowns players touched me, it was going to be a straight penalty."
Abafana Bes'thende, who were at the league summit in September, have spent much of the campaign in the top-eight. With title contenders Bidvest Wits coming up on Tuesday at Bidvest stadiam, Sibiya says it'll be unjust if they fail to book a ticket to next season's MTN8 Cup.
"There's no team that is unbeatable because Wits came away in the first leg with the draw," he says.
"It'll be a 50-50 game. If we can get four wins in the left matches I can tell you we'll likely finish in the top eight.
"We can't accept mediocrity after spending most of the time there and come end of the season our team is not there. Like what happened last season, where we were short with one point [to finish in the top eight]... we'll not accept such a repeat again."