Ramharack, Dottin star as West Indies level series
Five of the hosts' bowlers claimed a wicket, with Qiana Joseph's four-over spell of 0/19 helping the home side restrict South Africa to 80/9 from their allotted overs.
In response, Deandra Dottin (31) and Kyshona Knight (26) led the way to chase down the target with 49 balls to spare, to end the series on level terms.
South Africa won the toss and elected to bat, selecting the same eleven after their convincing second T20I victory. The day started poorly for the hosts, with Dane van Niekerk out caught behind for a duck off the bowling of Chinelle Henry inside the first over.
South Africa failed to recover from the early loss of their captain, with Aaliyah Alleyne ripping through the rest of the top order, claiming Lizelle Lee (9) and Marizanne Kapp (0) in the second over, leaving the tourists in a hole at 9/3.
After a dangerous knock in the back end of their second T20I innings, Laura Wolvaardt (3) had no such luck this time around, run out by Anisa Mohammed, with the help of 'keeper Kycia Knight.
Tazmin Brits (16) and Sune Luus (23) showed respite in a South African recovery, though fell to the West Indian spin pair of Hayley Matthews and Mohammed respectively, leaving the tourists stuck at 60/6 after 14 overs.
Though it was another spinner, Karishma Ramharack, who nipped any idea of a counter in the bud. She finished with 3/8 from three overs, claiming the dangerous Chloe Tryon (9), Trisha Chetty (6) and Ayabonga Khaka (1).
Despite the early loss of Matthews to Khaka (7), Dottin and Knight ruined any chance of a South African come-from-behind victory, putting on a partnership of 53 in six overs before Dottin was run out by Lizelle Lee.
Van Niekerk's leg-spin claimed the wickets of Kyshona Knight and Britney Cooper (0), though it mattered little in the context of the match, as Chedean Nation (8*) and Henry (1*) ensured victory for the hosts.
The teams now turn their attention to the ODI series, which begins on Tuesday.