Hargreaves replaces Johann Muller, who was ruled out after further evaluation on his hamstring strain during training.
Muller had not recovered sufficiently to take his place in the team.
"The new caps had outstanding Super Rugby seasons and this is an exciting opportunity for them. They have been rewarded for their form and now it's up to them," said Bok coach Peter de Villiers.
The world champions will be led by John Smit, in his 103rd Test and the skipper is confident that the two newbies (Greyling and Kruger) will fit well into South Africa's front row.
"We have got some new combinations, but there is a lot of potential in this side and the players are hungry for this chance," added De Villiers.
The South Africans are prepared for a fiery Australian side whom will be looking to make up for their 32-23 loss to Samoa. Seven regular Wallabies were missing from Sunday's defeat.