Australia's combination a mystery for Sydney

Spinners Ashton Agar and Steve O'Keefe have joined Australia's squad for the third Test in Sydney, but the final make-up of the XI remains a mystery three days out from the match. The one certainty is that Australia will use their fourth No.6 of the Test summer, with Mitchell Marsh, Callum Ferguson and Nic Maddinson all having been dropped after struggling in the position.

Seam-bowling allrounder Hilton Cartwright, who averages 44.50 in his short first-class career so far, could be in line for a Test debut at No.6, which might allow Australia to play two frontline spinners - Nathan Lyon and O'Keefe, perhaps - and two specialist fast men. However, another option would be to move wicketkeeper Matthew Wade up to No.6, despite his low Test scores this summer, and include Agar as a spinning allrounder.

That could then mean the three fast bowlers - Mitchell Starc, Josh Hazlewood and Jackson Bird - all playing alongside Lyon and Agar. Such a move would be a considerable vote of confidence in Agar, who famously made 98 batting at No.11 on Test debut at Trent Bridge in 2013. In the next Test, Agar batted at No.8, and since then has scored two first-class hundreds and averages 26.41 with the bat.

"I think I would be able to if I was given that opportunity," Agar said when asked if he could bat in the top seven of a Test order. "You just have to make good decisions, and that's what I'm learning more and more each time I'm batting in first-class cricket, is the best players consistently make good decisions. All the batters have the skills, but what separates them is who makes good decisions.

"I see myself as an allrounder. I guess I've been selected into this squad as a spinner, but I think I'm capable with bat and ball."

The inclusion of three spinners in the 13-man squad for the Sydney Test comes after plenty of turn was on display in Sheffield Shield matches at the SCG earlier in the summer. Notably, in the game between New South Wales and Western Australia in the first week of November, Agar finished with match figures of 10 for 141 and O'Keefe collected 8 for 106.

O'Keefe's selection comes at the end of a frustrating year for the left-arm spinner, who played in the Sydney Test against West Indies in the first week of January, which was severely affected by rain. He also played in the first Test in Sri Lanka in July and picked up three wickets - as he had in Sydney - but suffered a hamstring injury and was replaced by Jon Holland for the remainder of the series.

"I'd love nothing more than to play a full series and show my worth," O'Keefe said. "I'm not getting any younger and there's some great young talent out there. I know that this is probably my window where I've got to get it right, keep the body fit and bowl well. This is my opportunity. I'm excited about that."

O'Keefe hopes he will be given the opportunity to bowl alongside his New South Wales team-mate, Lyon, in the Sydney Test, after Lyon bounced back from a difficult summer to claim three vital wickets in Australia's fifth-day victory over Pakistan at the MCG.

"He's a guy that I look up to," O'Keefe said. "He's been super impressive his whole career. He's a really humble guy who gives a lot of time to players like myself and just a good all-round person to be around. I love playing cricket with him and I love bowling in tandem with him.

"He's had a lot of pressure but I think it's been a series that's been predominantly dominated by fast bowling. I think he's actually bowled really well. Last night's rewards were what he needed, and I think it just vindicates that he is bowling well. The wicket still wasn't doing much and he was able to crack the game open through the middle, knock over their experienced players and give their team a chance. That was great to see."