Morris' fiery spell follows Whiteman's 193 as Western Australia close in on big win

In-form speedster Lance Morris tore through South Australia late on day three to leave Western Australia on the brink of victory at the WACA.

After gaining a 145-run first innings lead, mostly due to centuries from openers Sam Whiteman and Cameron Bancroft, defending champions WA effectively ended the Redbacks' resistance with a stunning onslaught from their seamers amid the shadows at the WACA.

Watching the carnage from the other end was opener Henry Hunt, touted as a future Test player, who finished 27 not out and he will need to produce something special on day four if South Australia are to stave off defeat.

Morris continued his spectacular season with a fiery late burst to claim three wickets as he conjured sharp bounce and rapid pace to liven up what had been a rather sedate day's play. The 24-year-old, who is tipped to be part of Australia's T20I renewal, has taken seven wickets for the match and 22 overall this Shield season.

Seamer Matt Kelly, who took five wickets in the first innings, triggered the collapse with the scalps of opener Jake Weatherald and Daniel Drew.

On an overcast and cool day, continuing Perth's mild spring though Melbourne's weather was more of a talking point amongst those in the terraces, South Australia had initially fought back through their accurate seamers.

A green tinge on the WACA pitch was notable, but there was little of the rampant movement evident from the WA-Queensland Shield match earlier in the month where a remarkable 20 wickets fell on day two.

Starting at 0 for 256, Bancroft and Whiteman eyed WA's highest-ever first-wicket partnership of 431 by Mike Veletta and Geoff Marsh in 1989. But they were shackled during an attritional morning session by Wes Agar, who consistently threatened to break through.

Bancroft and Whiteman, however, remained unruffled as they passed South Australia's first innings total and crossed 300 to hearty applause from the smattering of fans.

They appeared well poised to bat through a third straight session until Bancroft's 324-ball knock ended when he played on to the hard-working Agar. The 308-run partnership was WA's fifth-highest opening stand, but it was followed by the home team collapsing after lunch.

Agar was further rewarded after knocking over in-form Hilton Cartwright with a pearler that hit the top of off stump leaving Whiteman, who made a pair against Queensland, to take charge.

He passed his highest First Class score of 176 not out - struck against Tasmania 12 months ago - as a maiden double century beckoned. Whiteman, however, wasn't focused on personal milestones as he attempted to lift the run rate after South Australia's quicks had restricted him by bowling full and wide.

He countered successfully by scooping pacer Liam Scott to the boundary, but his counterattack ended three balls later as Whiteman trudged off to a standing ovation from the WACA faithful.

After South Australia's bowlers had toiled for over 100 overs without reward, wickets came in a flourish with WA looking to accelerate.

Offspinner Ben Manenti was the recipient with his first five-wicket haul in First Class cricket, including Josh Inglis who fell for 22 in his first Shield match since missing out on the T20 World Cup after a freak injury playing golf.

South Australia suffered an injury blow when quick Jordan Buckingham damaged his right hand during a fielding mishap. And it went from bad to worse for them a big defeat looming early on day four.