The visitors from Pretoria held a 9-7 lead at the break in Mbombela Stadium, but three second half tries saw the home side take the initiative and lead to claim the first win of the 2019 tournament.
The match in the North Section of the competition started with a bang as fullback Devon Williams opened the scoring with a well-worked try. iSG Pumas flyhalf Chris Smith made no mistake as he added the extras.
The Vodacom Blue Bulls had to rely on the boot of JT Jackson (flyhalf) to gain ascendency, with three penalty goals giving them the lead at the break.
The iSG Pumas struck early in the second half, with two tries in the opening ten minutes. Willie Engelbrecht (No 8) dotted down, followed shortly by his loose trio partner Francois Kleinhans. Smith converted the latter's try for a 21-9 lead.
Smith added a penalty goal before outside centre Alwayno Visagie scored the bonus point try, duly converted by Smith.
Credit to the Vodacom Blue Bulls, who kept plugging away and was rewarded with two late tries. First Jackson dotted down, before Springbok and Blitzbok speedster Cornal Hendricks got his team back in the match with his first try in the competition.
The iSG Pumas kept the visitors at bay till the final whistle.
iSG Pumas 29 (7) - Tries: Devon Williams, Willie Engelbrecht, Francois Kleinhans, Alwayno Visagie. Conversions: Chris Smith (3). Penalty: Smith.
Vodacom Blue Bulls 21 (9) - Tries: JT Jackson, Cornal Hendricks. Conversion: Jackson. Penalties: Jackson (3).