Australia sealed their place in Sunday's final of the 50-over World Cup against India following a nervy three-wicket victory against South Africa in the second semifinal on Thursday.

Australia bowled out South Africa for a below-par 212 despite David Miller's defiant 101 but the chase was not as straightforward as Pat Cummins and his team would have liked.

Travis Head (62) led Australia's rollicking start before a mid-innings wobble put the five-time champions in a spot of bother.

Head and David Warner, who hit 29, started strongly before South Africa struck back.

Aiden Markram bowled Warner and Kagiso Rabada sent back Mitchell Marsh for a duck as Head, who was dropped on 40 and 57, looked to bat on.

However, Australia were in trouble at 137-5 after Keshav Maharaj bowled Head and fellow spinner Tabraiz Shamsi struck twice in quick succession.

The left-arm wrist spinner trapped Marnus Labuschagne lbw for 18 and bowled Glenn Maxwell for one in his next over.

South Africa did not let big partnerships bloom but Australia eventually reached the target with 16 balls to spare with Steve Smith (30) and Jos Inglis (28) providing useful cameos.

Earlier, Temba Bavuma's decision to bat under an overcast sky backfired and South Africa slumped to 24-4 inside 12 overs before light rain held up play.

Miller and Heinrich Klaasen (47) arrested the slide after play resumed with a 95-run partnership but Head's double strike put Australia back in charge.

Miller smashed Cummins for a six to bring up his hundred but fell in the same over trying to clear the rope again.

India beat New Zealand in the first semi-final on Wednesday to book their place in the final in Ahmedabad.