Quade Cooper seems to have secured the No.10 jumper © Getty Images

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New Zealand gain strength from their stable midfield combination, Stirling Mortlock says © Getty Images

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Ewen McKenzie must cease tinkering with the Wallabies backline if he is to forge combinations over the next month for Rugby World Cup 2015, Stirling Mortlock says.

Mortlock says Australia must take a leaf out of the All Blacks' book by settling on a 10-12-13 partnership - after six seasons of chopping and changing in the midfield under Robbie Deans - but McKenzie faces a tough immediate call at second five-eighth for the start of what Mortlock sees as a crucial Grand Slam tour when they play England in a Cook Cup Test at Twickenham on Saturday.

Matt Toomua's fine display at No.12 in the 41-33 loss to the All Blacks, in the third Bledisloe Cup Test in Dunedin, mixing and matching well with first-five Quade Cooper, has him challenging Brumbies team-mate Christian Leali'ifano for the jumper. Leali'ifano has overcome an ankle injury to set up a 50-50 selection call, with the outcome to be announced on Thursday.

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Mortlock played with both Toomua and Leali'ifano at the Brumbies, and finds it hard to split them presently, but he stressed the time had come to bed down a midfield combination. He also said the next five Tests should decide whether newcomer Tevita Kuridrani retains the outside centre position at the expense of Adam Ashley-Cooper.

Deans never got close to bedding down his best centre partnership after taking the reins in 2008, a year after Stephen Larkham's retirement ended his well-grooved combination with Matt Giteau and Mortlock. By contrast, Mortlock pointed to the Ma'a Nonu-Conrad Smith centre partnership as a cornerstone to New Zealand's success over the same time.

"You look over five to eight years, we haven't had set combinations for a while," Mortlock said. "Yet look at New Zealand they have had Nonu and Smith who have been the consistent, ever-presents in the midfield. It looks as though Ewen is settling on Quade [at five-eighth] but I don't think we've had a good combination at 10 and 12 with someone who's worked well with Quade, so that's going to be really key."

Christian Leali'ifano has regained full fitness after an ankle injury © Getty Images

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