Green was on 168 off 298 balls when WA declared at 5-409 on day three, giving South Australia a first-innings lead of 101.

The Redbacks finished the day at 4-142 - an overall lead of 243 - with one day remaining in the match.

South Australia were struggling at 4-61 in their second innings before Alex Carey (44no) and Harry Nielsen (46no) steadied the ship.

Green, who cracked an unbeaten double century for grade side Subiaco-Floreat last week, has now scored 531 runs at an average of 106.2 this Shield season.

The 21-year-old reached three figures late in Saturday's morning session, driving the 207th delivery he faced for a boundary.

Green, who made his Test debut at Adelaide Oval earlier this season and went on to entrench himself in Australia's XI, continued to score freely after the meal break.

His 183-run stand with Cameron Bancroft (126) has given WA a chance of snaring an unlikely win.

"Bangers is so good. I haven't really had the chance to bat with him before," Green said of Bancroft.

"His stroke play is a lot better this year I think. In years gone by, he was probably a bit too defensive. I'm really proud of the work he's been putting into training, and it paid off today."

Green was thrilled with his own knock, and revealed he had made an effort to play more strokes to different parts of the ground.

"I think I got a bit too one-dimensional in the Test series maybe, so I'm trying to get back to what I was doing well before," he said.

SA skipper Travis Head's career-best 223 had marched his side to a first-innings total of 8(dec)-510.

Australian Associated Press