Returning Stormer Peter Grant struck a penalty four minutes from time to secure a vital 15-12 victory over the Sharks at Newlands on Saturday.
In a result that was heading for a draw, it had looked like the hosts would be left to count the cost of four missed attempts from Joe Pietersen.
But up stepped Grant from the left-hand touchline as he knocked over a difficult penalty after Sharks captain Keegan Daniel entered a ruck illegally.
Victory propels the Stormers up to fourth in the overall standings, level on points with the Reds and one behind the pace-setting Bulls.
The derby fixture was short on entertainment yet rich in intensity as both XVs brought the physical.
With two thirds of possession in their pocket, the Sharks were worthy of their 9-6 half-time lead in a 40 minutes that saw the Stormers struggling for any real dominance on home soil. Inside centre Jean de Villiers was captaining the side in the absence of inspirational leader Schalk Burger.
And the absence of flanker Burger was apparent as the Sharks, notably Marcell Coetzee, dominated the physical early on. Their pressure resulted in the opening points of the game on twelve minutes as Pat Lambie slotted over a penalty before Pietersen replied soon after.
The tight spectacle continued to be a tit for tat affair as then Pietersen was the man being countered as Lambie replied with 20 minutes on the clock. One sensed a pattern emerging.
Lambie was successful with a long-range effort three minutes before the break as he made up for an earlier shot that struck a post. It was a deserved advantage to take into the break.
Cue a switch in momentum as, in a complete reversal of the first-half, it was now the Stormers who dominated both the possession and territorial statistic in Cape Town.
Grant, who was back from playing in Japan, emerged from the sideline as a replacement for Gary van Aswegen in the 48th minute and that proved to be the catalyst for the hosts.
Pietersen soon atoned for earlier lapses with a 55th minute penalty when the Stormers' pressure started to take its toll and at 9-9 Pietersen was unsuccessful from the tee before lock Ross Skeate was sent in the sin-bin. Pietersen held his nerve to make it 12-9.
But then the moment that all Stormers fans were concerned about arrived as Pietersen's missed attempts looked to have come back to haunt their side, with Lambie levelling.
Although the Stormers continued to hold the upper hand in the dying minutes, their efforts couldn't produce a try, but Grant stepped up two minutes from time to send over the winner.
Pen: Pietersen 3, Grant 2
Pen: Lambie 4
Stormers: 15 Joe Pietersen, 14 Gio Aplon, 13 Juan de Jongh, 12 Jean de Villiers (c), 11 Bryan Habana, 10 Gary van Aswegen, 9 Dewaldt Duvenage, 8 Nick Koster, 7 Duane Vermeulen, 6 Siya Kolisi, 5 Andries Bekker, 4 Eben Etzebeth, 3 Brok Harris, 2 Tiaan Liebenberg, 1 Steven Kitshoff.
Replacements: 16 Scarra Ntubeni, 17 Frans Malherbe, 18 De Kock Steenkamp, 19 Nizaam Carr, 20 Louis Schreuder, 21 Peter Grant, 22 Gerhard van den Heever.
Sharks: 15 Riaan Viljoen, 14 Louis Ludik, 13 JP Pietersen, 12 Meyer Bosman, 11 Lwazi Mvovo, 10 Patrick Lambie, 9 Frederic Michalak, 8 Keegan Daniel (capt), 7 Marcell Coetzee, 6 Jacques Botes, 5 Ross Skeate, 4 Steven Sykes, 3 Wiehahn Herbst, 2 Bismarck du Plessis, 1 Dale Chadwick.
Replacements: 16 Craig Burden, 17 Jannie du Plessis, 18 Anton Bresler, 19 Lubabalo Mtembu, 20 Charl McLeod, 21 Marius Joubert, 22 Paul Jordaan.
Referee: Mark Lawrence (South Africa)
Assistant referees: Jason Jaftha (South Africa), Christie du Preez (South Africa)
Television match official: Gerrie Coetzee (South Africa)