Sharks booted their way to a four-point lead at the top of the South African Currie Cup table Friday by edging Bulls 18-16 in Pretoria.
The Durban outfit have 32 points and title-holders Western Province 28 and they clash in the final league round next weekend with first place up for grabs.
Topping the table means a home semi-final on October 19 against the fourth-place finisher and, if successful, home advantage in the final one week later.
Bulls' losing bonus point moved them up one place to fourth and they play Cheetahs next in a game set to decide which team makes the knockout stage.
Sharks fly-half Fred Zeilinga slotted four penalties and replacement Butch James two, including the match-winner two minutes from time.
Trailing for most of the match, Bulls moved four points ahead before James kicked two penalties in the final nine minutes.
Youthful Zeilinga, who began the season as understudy to 2007 Rugby World Cup winner James, is now first choice and the leading Currie Cup scorer with 85 points.
The only try came from Bulls centre Francois Venter with fly-half Handre Pollard converting and kicking three penalties at Loftus Versfeld stadium.
Sharks led 9-6 at half-time after Zeilinga missed two kickable penalty shots, and triumphed despite having flanks Jacques Botes and Jean Deysel sin binned.
Botes, 32, was making a record-equalling 142nd appearance in rhe premier South African rugby competition and had an eventful match.
Forced to leave the field on 17 minutes with blood pouring from a facial wound, he returned only to be sin-binned soon after for a ruck infringement.
Former Springboks and Free State Cheetahs centre Helgard Muller held the Currie Cup appearances record for 15 years.