Ryan Harris is rested due to his hamstring strain, as captain Michael Clarke says it was hard to leave Shaun Marsh out after his century on debut.
Australia drop Khawaja for returning Ponting in third Sri Lanka Test
Harris, the most successful bowler in the series with 11 wickets, suffered a hamstring strain during the drawn second Test in Pallekele, and will be replaced by Peter Siddle.
Left-handed Khawaja was dropped to make way for former captain Ricky Ponting, who returns to the side after taking leave from the Pallekele Test for the birth of his second child.
Michael Clarke, the touring captain, and the selectors, had a tricky decision to make after Shaun Marsh, who replaced Ponting in the second Test, scored a century on debut to cement his place in the side.
"It's brilliant to have Ricky back, he was always going to walk back into the team," Clarke said ahead of a practise session at the Sinhalese Sports Club (SSC) today.
"It is hard for Uzzie [Khawaja]. It's obviously been a tough selection, but with Shaun making 141 on debut, it was really hard to leave him out."
Clarke said resting Harris was a precautionary measure considering the heavy schedule ahead, which includes Test series against South Africa, New Zealand and India.
"I guess we have to be safe, rather than sorry," the captain said. "I certainly don't think it's worth the risk of playing him here, because if that minor strain becomes a big tear he could be out for a lot longer."
Clarke said Australia's 1-0 lead in the series after winning the opening Test in Galle by 125 runs had put the onus on Sri Lanka to call the shots.
"Our goal is to win the Test, but if we draw, we go home 1-0 winners," he said. "But there is probably a bit more pressure on the Sri Lankans, knowing they have to win to level the series.
"They have to bat a bit more positively than they have done in the series so far and try and get a result."
If the hosts need inspiration, they need look no further than their former captain Kumar Sangakkara, who makes his 100th Test appearance.
Sangakkara, who turns 34 next month, will be the fifth Sri Lankan to play a century of Tests after Muttiah Muralitharan (132 matches), Mahela Jayawardene (121), Chaminda Vaas (111) and Sanath Jayasuriya (110).
Clarke paid rich tributes to the prolific left-hander, but hoped Australia will get him out early.
"I've enjoyed watching him score runs for a long time," said Clarke. "But I don't like it when he scores them against Australia and I hope he gets a pair [two ducks] in this game."
In the 18 Tests Sangakkara has played at the SSC, he has scored 1,864 runs at an awe-inspiring average of 74.56, with seven three-figure knocks, including three double centuries.
It was at the same venue that Sangakkara (287) and Jayawardene (374) recorded the highest partnership ever in Test cricket: 624 for the third wicket in 2006 against South Africa.
But Sangakkara has never featured in a Sri Lankan Test win over Australia, something the star batsman hoped to rectify.
"The key is to score big in the first innings, which we have not been able to do in the two Tests so far," said Sangakkara, who met the media instead of skipper Tillakaratne Dilshan.
"I think we have a good enough team to win on any wicket. It is always challenging to play the Aussies, but we have not challenged them enough in the series.
"I hope that will change here."