WA snared 7-53 late on the final day to secure the 36-run win with just seven balls to spare.

Paceman Matt Kelly was the hero on day four with figures of 5-63, while David Moody also played a crucial role and claimed three wickets.

Chasing 345 for victory off 70 overs, the Redbacks were on track after moving to 3-255 in the 55th over.

But the loss of Callum Ferguson (123 off 154 balls) and Tom Cooper (47 off 69) within six balls of each other killed off the visitors hopes of an upset.

Their dismissals sparked a massive collapse, with WA players celebrating wildly when Adam Zampa (37 off 31 balls) hooked Moody to fine leg to end the contest.

WA's Ashton Agar provided the highlight of the day when he pulled off a stunning one-handed catch at point to dismiss Redbacks opener Henry Hunt.

"It's a great feeling, It was a really important win for our season," Kelly said.

"It's good to take wickets, but more importantly, it's good to contribute to the team.

"It's really exciting four-day cricket when it pans out like that."

Earlier, WA veteran Shaun Marsh cracked an unbeaten 102 to lift the home side to 6(dec)-205 in their second innings.

WA started the final day at 4-70 and needing some quick runs to ensure they could build a massive lead and give themselves enough time to bowl South Australia out.

Marsh, who was on 32 overnight, ensured the runs kept ticking over, as he and Agar (45no) combined for a quick-fire 94-run stand.

Marsh's century came less than a week after he hit an unbeaten 101 to guide WA to victory in the Marsh One-Day Cup Final against Queensland.

The win sees WA move up into third place on the Sheffield Shield ladder, just three points behind Queensland.

Western Australia face Victoria in their next Shield match, starting on Saturday 7 December at the MCG.

It's the final round of Sheffield Shield fixtures before the KFC Big Bash League gets underway later this month.