An 80th minute Sharks try for a 22-20 victory put a major and probably fatal dent in the Blues' Super 15 playoff prospects.
After an awful first half effort, the Blues bounced back from a 5-17 deficit to lead by 20-17 in the dying moments of the match at Kings Park in Durban.
The South African strugglers - whose coach John Plumtree departed just days before the match - launched a series of drives at the Blues line before spinning the ball wide to Riaan Viljoen who ducked inside Rene Ranger's covering tackle to clinch the victory.
In a scrappy, low-quality game, the Sharks owned the first half and repeatedly smashed the Blues scrum throughout the 80 minutes. But the home side lacked penetration and suffered through a horror goalkicking effort from Patrick Lambie, who landed three from eight attempts.
In contrast, the Blues looked the more dangerous with ball in hand, but didn't give themselves enough opportunities to make enough of that advantage.
The Sharks took 20 minutes to profit from their early dominance, and they scored a second try on the half hour mark through their lively halfback Charl McLeod.
The Blues' first attack of the match brought a try to the power wing Frank Halai.
The Blues lifted their game in the second half and scored again through Halai, who swatted off Lambie on the way to the tryline. Ranger then drew the Blues level, grabbing the ball from a ruck near the Sharks line soon after being sent on by coach John Kirwan in the 45th minute.
A Baden Kerr penalty edged the Blues in front, setting up the tense final minutes.
The Sharks hurled themselves at the Blues defence, with acting captain Bismarck du Plessis turning down a simple penalty shot in order to go for the winning try.
If Lambie was the villain for the Sharks, Blues first five-eighths Chris Noakes had an opening stanza to forget, having a kick charged down, putting a kickoff into touch, and then missing touch from a penalty.
The result left the Blues outside the top six and unlikely playoff participants with two rounds to play. They meet the sixth place Cheetahs in the next round before taking on the champion, in-form Chiefs.
The Cheetahs will get an automatic four points from their last round bye.
Sharks 22: (Marcell Coetzee, Charl McLeod, Riaan Viljoen tries; Patrick Lambie 2 con, pen)
Blues 20: (Frank Halai 2, Rene Ranger tries; Chris Noakes con, Baden Kerr pen).
Halftime: 17 - 5.