SYDNEY, AUSTRALIA - JULY 21: Jacques Potgieter of the Waratahs runs with the ball during a Waratahs Super Rugby training session at Moore Park on July 21, 2014 in Sydney, Australia. (Photo by Matt King/Getty Images)

Sydney - Jacques Potgieter will start at lock for the New South Wales Waratahs in this weekend's Super Rugby semi-final against the ACT Brumbies but coach Michael Cheika thinks Will Skelton could be a matchwinner from the bench.

Hard-running former Springbok Potgieter has got the nod alongside Kane Douglas in the second row for Saturday's match at Sydney Football Stadium, which will decide who faces the Canterbury Crusaders or South Africa's Sharks in the final.

Cheika, though, expects all three of his locks to have a big impact on the Australian derby, not least the 22-year-old Skelton, who is almost certain to win one of the spots on the bench.

“Rugby has changed so much, back in the day you'd have to be injured to be taken off. Now the replacement players are the matchwinners,” he told reporters.

“So it's got a whole new scope about what happens and (Will) knows how important his role is.”

Skelton, who weighs in at 140kgs but has shown soft hands with the ball that belie his huge frame, impressed on his test debut against France in June and has been hailed as one of the future stars of Australian rugby.

“Ah mate, that's footie,” Skelton told reporters. “I'd love to start but whatever my role is in the team I'll try and provide impact.

“If that's on the bench this week, I'll do my best for the team. Cheik's harped on about it all year, when the bench comes on it's an impact thing, you've got to lift the intensity.”

Fullback Israel Folau and winger Rob Horne both return to the side after missing the final match of the regular season against the Queensland Reds because of a thigh problem and flu respectively.

“I missed the last game against the Reds. The body's feeling fresh and I'm ready to go,” said Folau, who has scored a competition-leading 12 tries in 12 games this season.

There will be no place among the replacements for Peter Betham, though, with Cheika feeling the winger needed more time at club level after 14 weeks out with a broken foot.

“He was giving me the daggers down there when I told him the team,” said Cheika.

“I just think he needs to get a run under his belt... nothing can replace getting on the field and playing.

“Hopefully, we'll have to make another selection next week and he'll be a chance then.”

Team: Israel Folau, Alofa Alofa, Adam Ashley-Cooper, Kurtley Beale, Rob Horne, Bernard Foley, Nick Phipps, Wycliff Palu, Michael Hooper, Stephen Hoiles, Kane Douglas, Jacques Potgieter, Sekope Kepu, Tatafu Polota-Nau, Benn Robinson.