WA declared at 5-481 after the middle-order pair pummelled the SA attack during the first session and a half.

But Adelaide's Karen Rolton Oval proved just as bountiful for the home side, Jake Weatherald (104 not out) bringing up his ton just before stumps as SA finished the day at 1-178 in response.

Earlier Inglis (153) had also remained unbeaten for WA, clubbing 26 boundaries and three sixes in the impressive 182-ball knock.

It was his first ton in 35 first-class games.

Tweaker Agar, who famously scored 98 on debut for Australia against England batting at No.11 in 2013, remained not out on 114.

It was just his third first-class century and biggest of his career.

Agar said he enjoyed moving up the batting order and would like to come in at No.6 in the future.

"I was stoked when I got the opportunity to go and do it," he said.

"I had a think about how I was going to approach it.

"But really I've batted at seven and made a hundred at seven before so I just had to go about it the same way as I would every innings: get in, get started, get set and make good decisions from there."

After taking all the wickets on day one, Lloyd Pope remained the most likely of the SA bowlers but grew increasingly expensive to finish with 5-164 off 27 overs.

Weatherald and Henry Hunt (57) capitalised on the benign conditions when SA took to the crease, compiling a 125-run first-wicket partnership.

Cameron Gannon (1-43) claimed what would be the only scalp of the day when Ashton Turner caught Hunt sharply at short midwicket.

Agar had a busy day for WA, putting in a 14-over spell (0-53) while Joel Paris (0-34) and Matthew Kelly (0-32) also toiled fruitlessly.

Australian Associated Press