Plenty of bowling pressure from WA saw the visitors struggle to form meaningful partnerships and SA lost their first four wickets for just 44 runs.
Earlier, Amanda-Jade Wellington and Tahlia McGrath were impressive with the ball, taking four wickets each, but WA's batters worked hard, with Nicole Bolton (94) leading the pack.
WA openers Chloe Piparo (42) and Ashley Day (45) provided an excellent platform for their side, putting on 71 runs before the former was bowled by Wellington (4/31).
McGrath (4/40) finally removed Bolton just shy of her century, but the bulk of the damage was already done.
An economical, yet wicket-less, spell from captain Megan Schutt (0/32) still saw WA finish with a competitive 9/259.
South Australia lost McGrath in the first over for a duck but Bridget Patterson (23) and Eliza Doddridge (14) looked to be consolidating well, before Doddridge was bowled.
The WA bowlers continued to pile on the pressure, with SA managing to compile just nine runs from the next five overs following Doddridge's dismissal.
Annie O'Neil (duck) and Tegan McPharlin (9) both fell cheaply but Wellington toiled hard, striking four boundaries as part of a 38-ball 32.
Schutt (15 not out) and Darcie Brown (19) showed fighting spirit, combining for a 39-run stand for the final wicket.
Brown was eventually bowled in the 41st over and SA was all out for 157.
The Scorpions will take on WA again on Thursday from 12:30pm ACDT at the WACA.