Redbacks eight wickets away from back-to-back Shield wins

South Australia remain well placed for a rare win over Marsh Sheffield Shield ladder leaders Western Australia despite an unbeaten half-century from Cameron Bancroft keeping alive the visitors' hopes of chasing down a massive victory target at Adelaide Oval.

WA ended the penultimate day at 2-139 in pursuit of an unlikely 468 to win.

Bancroft remains is on 79 having found the boundary on eight occasions.

Hilton Cartwright is also at the crease on 23, with plenty of batting still to come for WA in the form of Aaron Hardie, Josh Inglis and Marcus Stoinis.

WA lost opener Sam Whiteman caught behind off Nathan McAndrew for 17, and the important wicket of veteran Shaun Marsh caught at second slip for 16.

Bolstered by the returning Stoinis and Marsh, WA started the match as warm favourites having already accrued four wins from six matches.

South Australia, in contrast, collected just one win during the first part of the season before the break.

Earlier, South Australia made the most of their 276-run first innings lead to pile on quick runs in search of a declaration.

Nathan McSweeney made it two centuries in as many matches for the Redbacks, hitting 104 not out with 13 boundaries and a six in his 131-ball stint at the crease.

SA resumed at 2-31 but McSweeney's counter-attack ensured the home side kept their run-rate high.

There were also contributions from Henry Hunt (27), Jake Lehmann (18) and Thomas Kelly (18) as SA posted 6(dec)-191.

Only seamer Matthew Kelly threatened to halt the local sides' charge, taking 3-38.