The right-arm spinner claimed 6-79 to complete a match haul of 11-107 to ensure the hosts levelled the series 1-1.
The decisive third match between the sides will take place in n Bloemfontein next week.
SA A started the day at Buffalo Park needing five wickets to win and Piedt took the first scalp of Kevin Sinclair, caught for 21.
Abhijai Mansingh (five) was the next batsman to fall within the space of three overs to Dane Paterson (1-44).
Tevin Imlach (34) followed after a sharp throw in from Raynard van Tonder fielding at point, which left the batsman short of his ground at the non-striker’s end, leaving the visitors on 164-8 within the first hour of play.
Akeem Jordan (21) and Shamar Joseph (18*) combined to take the West Indies A past the 200 mark.
However, Piedt soon wrapped up the innings with two wickets in two overs as the visitors were bundled out for 209.
Photo: Lee Warren/Gallo Images
