Defending champions WA lost 8-48 as they crashed from 2-72 to be rolled for 120 on a testing wicket on Saturday.
In reply, the Redbacks were bowled out for 124, with WA paceman Brody Couch (4-33) the chief destroyer.
WA opener Sam Fanning (49) got the home side off to a solid start, but he played a lone hand as Liam Scott (3-10 off 8.4 overs), Jordan Buckingham (3-35) and Brendan Doggett (2-24) feasted for the Redbacks.
Joel Curtis (15) and Ashton Turner (12) were the only other WA players apart from Fanning to make it into double figures.
Any thoughts of South Australia being able to build a big first-innings lead quickly evaporated, despite the best efforts of Jason Sangha (45 off 81).
Openers Conor McInerney (four) and Henry Hunt (15) weren't able to stick around for an extended period.
Sangha was a steadying force for the Redbacks, but they crashed from 2-53 to 124 all out as WA's attack wreaked havoc.
Couch led the destruction, while spinner Corey Rocchiccioli (3-10) and Joel Paris (2-34) were also among the wickets.
Cameron Gannon only took the one scalp, but it was a ripper of a delivery that kicked up and caught the glove of a surprised Sangha.
"It was a pretty big day, evenly poised," Couch said.
"It was just a wicket-fest today. Twenty wickets on day one - it's a bit unusual.
"Pretty nice conditions for the bowlers. Big job ahead to try to make as many runs as we can.
"There was plenty of sideways movement. We'll see how the pitch changes on Sunday."
The match shapes as crucial in the race to reach the March 26-29 final.
The Redbacks (29.93 points) sit on top of the ladder with three wins and two draws from six games, while WA (23.91 points) sit fourth with two wins and two draws from six outings.
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