Van der Westhuizen has made way for Sharks halfback Craig Davidson, while Cats five-eighth Andre Pretorius is the new fullback.
Pretorius takes over from Brent Russell, who proved the match-winner as a replacement against the Wallabies in Cape Town three weeks ago but struggled badly against the All Blacks.
Cats midfielder Jorrie Muller comes in to partner De Wet Barry in the centres in place of injured Andre Snyman.
Versatile prop Robbie Kempson and lock Selborne Boome start for the first time in this year's Tri-Nations while Cats loose-forward Joe van Niekerk will also play his first Test of the year after recovering from injury.
Van Niekerk replaces Wikus van Heerden at openside breakaway while Kempson comes in for Lawrence Sephaka and Boome takes over Bakkies Botha.
Straeuli said the changes are due to a combination of poor form and the need to give bench players more game time.
"There are players who have paid the price for an unacceptable performance against the All Blacks and there are players who have been rotated in our effort to establish a squad in which all players are capable of starting in any given Test during the World Cup," Straeuli said.
The Springboks coach is excited at what Pretorius offers at fullback.
"He is a wonderful attacking player and a very good kicker, which gives us more options in the latter department."
Springboks Team to Face Australia:
Andre Pretorius, Stefan Terblanche, Jorrie Muller, De Wet Barry, Ashwin Willemse, Louis Koen, Craig Davidson, Juan Smith, Joe van Niekerk, Corne Krige (capt), Victor Matfield, Selborne Boome, Richard Bands, Danie Coetzee, Robbie Kempson. Res: Dale Santon, Lawrence Sephaka, Bakkies Botha, Wikus van Heerden, Joost van der Westhuizen, Gcobani Bobo, Brent Russell.
On the Aussie Side:
Chris Latham replaces Matt Burke in the Australian team to meet South Africa in the Tri-Nations Test at Brisbane's Suncorp Stadium on Saturday night.
Burke was dropped to the bench in the only change to the starting team following Australia's 50-21 loss to New Zealand in Sydney last Saturday.
Selectors made three changes to the reserves bench, recalling hooker Jeremy Paul, prop Glenn Panoho and utility back Matt Giteau.
Adam Freier, Steve Kefu and injured prop Ben Darwin were left off.
Inside centre Elton Flatley will take over from Burke as goalkicker as the Wallabies try to avoid their fourth consecutive loss for the first time in 21 years.
Burke's hopes of overhauling Michael Lynagh as Australia's leading points scorer depend on his ability to push back into the starting team before the World Cup begins in October.
Burke, who has played 70 Tests, has 851 points.
Lynagh scored 911 points from his 72 Tests before his retirement in 1995.
Chris Latham, Wendell Sailor, Mat Rogers, Elton Flatley, Lote Tuqiri, Stephen Larkham, George Gregan (capt), Toutai Kefu, Phil Waugh, George Smith, Daniel Vickerman, David Giffin, Patricio Noriega, Brendan Cannon, Bill Young. Reserves: Jeremy Paul, Glenn Panoho, Nathan Sharpe, Owen Finegan, Chris Whitaker, Matt Giteau, Matthew Burke.