A Juan de Jongh try made the difference as the Stormers defeated the Sharks 22-15 in a forward-dominated Super 15 clash of South African sides.
Springboks centre de Jongh crossed the line on 35 minutes at Newlands to help the home team build a 16-6 half-time lead they successfully defended under intense second-half pressure.
The Sharks' only consolation was a stoppage-time penalty goal from fly-half Patrick Lambie that secured a losing bonus point in a return fixture after the Durban team won 12-6 at home last month.
The Stormers had the better of the scrum battle, taking several tightheads, were superior in the loose exchanges, and also stole several line-outs for a third win in seven outings this season.
The Sharks remain third overall and on top of the South African conference despite a second loss in seven matches, but will be disappointed at failing to turn early second-half superiority into more points.
They did have try-scoring chances, with selfish full-back Francois Steyn robbing them of a late first-half chance and Stormers replacement hooker Martin Bezuidenhout came to the rescue after left wing Sean Robinson broke clear.
Another key factor for the Stormers was the flawless goal-kicking of full-back Joe Pietersen, who kicked five penalty goals and a conversion for a 100 percent record.
Although not at his best in general play, Lambie was almost as successful as Pietersen when kicking at goal, slotting five of six penalty attempts and the one he missed was an ambitious effort from the halfway line.
Pietersen kicked three penalties to give Stormers a nine-point advantage before Lambie cut the deficit, only for Stormers to go 13 points clear when De Jongh dived over.
Flanker Michael Rhodes won a line-out at the tail and his burst forward set in motion a handling move that ended with a clever off-load from captain and centre Jean de Villiers for de Jongh to score.
A second Lambie penalty left 10 points between the teams at the break and the game was won and lost during the first 20 minutes of the second half, when the Sharks could not translate territorial dominance into significant points.
Pietersen kicked two penalties and Lambie three during the half to give the Stormers a crucial win as they play catch-up in the hope of making the play-offs once again.