It took two late goals from Bongeka Gamede and Jermaine Seoposenwe to decide a tight game from a very physical Zambian side.
Zambia made the more assertive start, with their attacking duo of Barbra Banda and Rachel Kundananji posing consistent problems for the South African defence - though their finishing let them down. Banda had an early effort deflected wide in the 10th minute, and later missed a headed opportunity from a corner just before halftime.
Banyana created a few half-chances, with Seoposenwe working tirelessly down the channels and looking to supply her teammates. Twice she delivered dangerous balls into the box for Amogelang Motau, but the midfielder was unable to convert - arriving late on one occasion and missing the target on another.
Zambia made the first change at halftime, bringing on teenage midfielder Mercy Chipasula for Ireen Lungu, while South Africa stuck with their starting lineup.
With 15 minutes remaining, Banyana were awarded a free-kick just outside the area after Ramalepe was brought down. Gamede stepped up and struck a superb effort that flew into the top corner to give South Africa the lead.
Seoposenwe then sealed the result in the 82nd minute, punishing a poor Zambian clearance to slot home from close range-her third goal of the series.
The win sees Banyana top the tri-series standings with six points, as they now turn their focus to defending their continental crown at WAFCON in Morocco this July.