Agar, the wunderkind of the 2013 Ashes tour, merited a place on the strength of 16 well-priced Sheffield Shield wickets in the first half of the season, including 10 against New South Wales at the SCG. O'Keefe has been the favoured left-arm option for some time, but must now prove his ability to stay fit for the lengths of time required following a string of calf issues.
"We wanted a left-armer to go away from all their right-handers as well to give us options," Australia's coach Darren Lehmann said of Agar. "He got 10 in Sydney [Sheffield Shield game]. He's improved, we get feedback from JL and the guys have been watching him, they've been impressed with him. The hardest thing we've got at the moment is no Shield cricket, so you go with a bit of BBL form as well. So they're not bowling as much as we'd like, but before that he was doing really well.
"[O'Keefe's] got to be fit and he's playing now so that's the main thing. He wouldn't want too many more injuries, he'd want to make sure he's playing cricket. That's the greatest thing we have now, young players coming through that are fit and ready to go. Stephen did a really good job in Sri Lanka for us before he got injured, did a really good job for us in Sydney as well, so he knows he's got to be fit and ready to play each and every game."
Lehmann spoke warmly of Nathan Lyon following his strong display on the final day of the MCG Test, particularly the greater consistency shown by Australia's most prolific off spin bowler. " I thought he was outstanding," Lehmann said. "He bowled consistent line and length, which was up and down in the previous few Test matches, and he got through the middle order so pleased for him.
"I was just pleased the way he bowled today, more so than fourth innings winning the game, and bowling that consistent line and length we've been after all summer. Three or four balls an over have been there, but today was a lot better."
Allrounder Hilton Cartwright has been retained in the squad, but there was no room for swing bowler Chadd Sayers, who had been part of the squad for the first two Tests against Pakistan. Lehmann said that Cartwright and Agar would both be under consideration in an allround role.
"If you play two spinners you normally need an allrounder, so that's what we're looking at," he said. "Agar genuine [allrounder], yeah. He's made Shield hundreds, and batted well in that Test match at 11, but certainly got the talent to be a batting allrounder or a spinning allrounder, either way."
Maddinson was axed after struggling for impact in the first three Tests of his career, with scores of 0, 1, 4 and 22 in his four Test innings so far. "He's still got a bright future," Lehmann said. "I thought he batted really well this game, he would've liked a bigger score. I thought he played well, got a start and could have gone on big and put pressure on the selectors."
Rather than recalling Shaun Marsh, Lehmann said the selectors had chosen to keep him playing T20 matches while retaining the services of the young Queensland opening batsman Matt Renshaw. "We decided to keep him playing BBL," Lehmann said. "Matt's done a reasonable job for us in the Test matches, so we're going to go with that same opening combination for the last one."
Squad: David Warner, Matt Renshaw, Usman Khawaja, Steven Smith (capt), Peter Handscomb, Hilton Cartwright, Ashton Agar, Matthew Wade (wk), Mitchell Starc, Steve O'Keefe, Nathan Lyon, Josh Hazlewood, Jackson Bird