Sharks ensured their place in the Super Rugby play-offs with a 40-29 beating of Sunwolves in Durban, but Waratahs' defeat at Blues leaves their chances hanging by a thread.
Gary Gold's Sharks headed into Friday's contest against bottom-of-the-league Sunwolves knowing that a win would leave Bulls unable to clinch the wildcard spot in the South African Group.
It was not a straightforward outing for a Sharks side that struggled defensively, but they ran in six tries to repel the spirited Sunwolves and extend their season.
JP Pietersen captained Sharks on his final home appearance and marked his farewell with a first-half try, while full-back Gareth April contributed 15 points in a fine performance.
The Tahs, meanwhile, sit in a perilous position after going down 34-28 at Blues. A losing bonus point lifts them top of the Australian Conference, but the Brumbies need just a point against Western Force - who have won just twice this season - on Saturday to return to the summit and end the Tahs' campaign.
In Friday's other contest, Rebels were 31-28 victors at Reds.
Blues 34-28 Waratahs
The Tahs had no shortage of attacking intent and scored four tries, but the Blues responded swiftly on each occasion. Blues had trailed twice, but after Piers Francis touched down on the right early in the second half, their lead was never relinquished. Israel Folau and former Blues forward Angus Ta'avao twice brought the Tahs within one, but they now need a big favour to reach the play-offs.
Reds 28-31 Rebels
Rebels levelled their best Super Rugby season by earning a seventh win of the campaign. The visitors looked on course for an easy win with Sean McMahon scoring two tries en route to a 24-7 half-time lead. However, the Reds - champions as recently as 2011 - fought back valiantly with Liam Gill going over twice. There was to be no dramatic revival, though, and the best Reds can hope for is a 15th-placed finish in the overall table.
Sharks 40-29 Sunwolves
Sharks came bursting out of the blocks with tries from Coenie Oosthuizen and Lwazi Mvovo in the first seven minutes, before Pietersen touched down after Kaito Shigeno had put the visitors on the board. But Sunwolves were just two points adrift at the break with Mifiposeti Paea and Takeshi Kizu touching down. However, Sharks added a further three scores in the second half to end the Sunwolves' challenge.
THE KEY MOMENTS
Sharks needed a quick start to the second half and Andre Esterhuizen's score in the 41st minute provided much-needed breathing space. Further scores from April and Curwin Bosch made sure of the win.
Blues reacted quickly to Folau and Ta'avao's tries with Melani Nanai and George Moala ensuring the hosts' enterprising performance was not in vain.
"Stranger things have happened, so we'll wait and see how it goes tomorrow night." - Waratahs captain Michael Hooper is remaining optimistic of a favour from Western Force.
"I'm feeling very happy, really good performance. The most important thing is we qualified for the play-offs. I was disappointed with our defence, we pride ourselves on defence. We have to fix it on Monday." - Pietersen wants Sharks to tighten up for the play-offs.
Sharks' victory means they are in the play-offs with Bulls having little to play for against Cheetahs on Saturday. Waratahs need a favour from Force to continue their season.