After a goalless first in which the home side had better chances at goal, Sundowns finally got a golden chance to take the lead.
Marvin Sikhosana handled inside the box while trying to block a Peter Shalulile cross to earn Masandawana a penalty which Lucas Ribeiro Costa converted in the 53rd minute.
Substitute Neo Maema then put the match out of Gallants' reach when he struck right at the death to contribute to sending Sundowns to the final where they will meet Magesi.