Israel Folau scored two minutes from time to finish off the Stormers in Sydney.
The hosts won 21-15.
The Waratahs, who led 8-3 at half-time, trailed 15-11 going into the final few minutes but Folau rewarded a positive approach with a converted try and replacement flyhalf Berrick Barnes completed the scoring with a 50 metre penalty on full time.
Folau’s brilliance in the air set up the only try of the first half and it was the former Rugby League sensation and Aussie Rules convert’s finishing that sealed the Stormers fate.
The Stormers, as has been the norm in the last few years, were brave, courageous and determined on defence, but never looked comfortable with ball in hand and not once threatened the Tahs tryline.
The Tahs, one of the best attacking teams in the competition, never stopped believing they had the attack to break down the visitors defence and the experienced Barnes created the Folau match winner with a delayed short pass that exposed Bryan Habana’s defensive alignment.
Habana is the intercept king but on occasion he concedes tries through rushing out of line and he backed himself for the intercept but Barnes’s decision-making beat Habana’s rush and Folau did the rest.
Barnes had a huge impact in the last quarter and this coincided with the loss, through injury, of the imposing and physical No 8 Duane Vermeulen.
The Stormers, celebrated for their defensive structure, have never looked like title contenders because of their inability to be equally impressive on attack.
Waratahs – Tries: Cam Crawford, Israel Folau. Conversion: Berrick Barnes. Penalties: Brendan McKibbin (2), Barnes.
Stormers – Penalties: Joe Pietersen (5).