The injury-hit NSW Waratahs have lost in-form prop Sekope Kepu and possibly centre Ryan Cross for next weekend's crunch Super Rugby clash with the Bulls in Pretoria.

Kepu lasted just 12 minutes and Cross 22, as both fell victim to knee injuries in the Waratahs 26-21 loss to the Sharks in Durban on Sunday morning (AEST).

NSW led 21-13 with 25 minutes to go when fullback Kurtley Beale kicked a penalty awarded after Sharks flanker Jean Deysel was sin binned for a choke hold on centre Tom Carter.

But the Sharks capitalised on the visitors' turnovers and poor discipline to score 13 unanswered points.

The result left the Waratahs wobbling on the finals tightrope with three rounds remaining.

The Sharks (47 points) displaced the Waratahs (46) from fifth with the Bulls (45) and Highlanders (44) still very much in contention.

Kepu suffered a medial ligament injury while Cross fell awkwardly after being hit by a high tackle off the ball.

"I think we are probably looking at three to four weeks for Sekope at his stage," NSW coach Chris Hickey told AAP by telephone from South Africa.

"Ryan Cross's problem isn't quite as severe as Sekope's but I think he would certainly be in doubt for the Bulls game."

NSW went into the match without a smattering of stars including their most dangerous back Drew Mitchell, star backrowers Wycliff Palu and Phil Waugh and five-eighth Berrick Barnes.

Barnes, who has suffered three head knocks this season, trained on Saturday and could be available to face the Bulls next Saturday morning (AEST).

Veteran Al Baxter will almost certainly replace Kepu.

Hickey was keeping his options open about the replacement for Cross, though he could switch Lachie Turner to outside centre and start Atieli Pakalani on the wing.

Pakalani missed a glorious chance to push NSW ahead with eight minutes to go when he won the chase to a Beale stab kick, but knocked on over the line.

Five-eighth Daniel Halangahu, who moved into the team on Friday for Barnes, shaped as the hero.

He set up a 95-metre breakout try to Turner in the first half and scored himself in the second after beating three defenders from a scrum move.

The Sharks dominated possession in the second half and powered home in the final quarter.

Springboks winger JP Pietersen sprinted over 60 metres for a match-changing try after pouncing on a loose pass from Beale.

Promising five-eighth Patrick Lambie, who scored 21 points, including a first half try, kicked two late penalties to secure victory.

"I think that we tried to play too much football in our own half and their defence was able to stop us there and we didn't build a lot of pressure on them," Hickey said.

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