Western Australia 355 and 3 for 115 (Short 56*) lead South Australia 201 (McInerney 51, Guthrie 4-59) by 269 runs
The Warriors began the day 269 runs in front and showed no mercy despite losing D'Arcy Short and Ashton Turner early on. Both men were caught behind off the bowling of Nick Winter.
But Cartwright and Ashton Agar added 136 for the sixth wicket. Agar made 86, his first half-century of the season, before becoming Winter's fourth scalp.
Cartwright got to a patient century, his first of the season after he was moved down the order from No. 3 to No. 6 following a lean period.
The Warriors showed no urgency in declaring, piling up a lead of 524 before sending the Redbacks in to face five overs late on day three.
Joel Paris had Conor McInerney caught at second slip off the second ball of the innings before Jake Weatherald and Callum Ferguson saw the home side through to stumps.
Alex Malcolm is a freelance writer based in Perth