After being sent in to bat by South Africa captain Temba Bavuma underneath overcast skies in London, Australia slumped to 2-16 after Rabada ran riot in the seventh over.
The Proteas quick, who recently served a one-match ban for testing positive to cocaine, removed Usman Khawaja (a 20-ball duck) and Cameron Green (four).
In his first Test since March 2024, fit-again Green hit his first delivery to the boundary at fine leg in a promising start.
But the 26-year-old was gone just two balls later, edging a Rabada rocket to slips where he was superbly caught by Aiden Markram.
Marnus Labuschagne, in his first innings as a Test opener, started brightly to get through until drinks.
But as he often has during the last two years, the under-pressure Queenslander struggled to keep the score ticking over.
Labuschagne got caught between playing a shot and leaving a Marco Jansen delivery, nicking off for 17 from 56 balls.
The 30-year-old, who was once described as having "opening-itis", won the battle to be Khawaja's fifth opening partner in 18 months over teenager Sam Konstas.
The spectre of Konstas, one of Australian cricket's rising stars, will loom large for the upcoming three-Test tour of the West Indies.
Labuschagne's last Test century came back in July 2023 at Manchester.
Travis Head, who starred with a matchwinning 163 in Australia's WTC final triumph in 2023, fell on the final ball before lunch.
Wicketkeeper Kyle Verreynne hung on to a screamer down leg side off Jansen's bowling to send Head (11) on his way.
Superstar Steve Smith (26*) will resume in the second session with allrounder Beau Webster, playing in just his fourth Test.
In the 2023 final win against India, Smith and Head put on a 285-run stand after coming together at 3-76.
Josh Hazlewood returned to partner fellow star quicks Pat Cummins and Mitchell Starc in his first Test since December.
South Africa, who won seven-straight Tests to qualify for the final, are attempting to break a title drought in ICC tournaments dating back to 1998.
"The more finals you play in, you obviously improve your chances of winning. It doesn't weigh heavy on us," South Africa coach Shukri Conrad said.
"It's unfair to burden this group with anything that's gone before.
"We know we want to and we need to win another ICC event, but whatever tags come along, we don't wear that."
This AAP article was made possible by support from Amazon Prime Video, which is broadcasting the World Test Championship final.
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