Smith, Mitchell Marsh heap pain upon England
Australia 4 for 549 (Smith 229*, M Marsh 181*) lead England 403 by 146 runs
Scorecard and ball-by-ball details
It would be hard to imagine a day of greater Australian dominance than this one. It was a day on which Steven Smith made his second Test double-century, Mitchell Marsh scored his maiden Test hundred, England claimed just a single wicket and Australia piled on 346 runs. A day that began with Australia trailing by 200 finished with them 146 runs in front, and with a realistic chance of pushing for victory - and the urn - over the next two days. Remind us why Australia would want to move Ashes Tests away from the WACA?
But a caveat is necessary, for it was not a day that necessarily ended England's campaign. The pitch remains good for batting - that is stating the obvious - and there is rain forecast over the next two days in Perth. It remains very possible that England will escape from this match with a draw, and as the holders of the Ashes, that would keep them alive in the series. Alive, but demoralised. They might have known that Smith could score a mountain of runs, but Mitchell Marsh eyeing off a Test double-century by stumps? They'd have been more likely to expect the Spanish Inquisition.
This was a day that can best be illustrated by the numbers, and at the close of play, the numbers were these: Smith was on 229, Marsh was on 181, and Australia had 4 for 549. Hundreds were also piling up in England's bowling analysis: Craig Overton, Chris Woakes, Stuart Broad and Moeen Ali had all conceded centuries by the close of play, and if James Anderson - currently at 0 for 85 - joins them on the fourth day, it will be just the eighth time in Test history that a team has had five or more bowlers concede 100 in the same innings.
Some more numbers: by stumps, the Smith-Marsh partnership was worth 301 runs, the most prolific partnership Smith has ever been involved in at Test level. And Marsh's score was already the sixth-highest of all time by an Australian No.6. Along the way, Smith passed 1000 runs in a calendar year for the fourth consecutive year, joining Matthew Hayden as the only men to achieve this feat, and Smith has done so averaging 60-plus in every year.
The day had started in vaguely reasonable style for England, when they claimed the wicket of Shaun Marsh, who edged Moeen to slip for 28. It was the only reason England had to celebrate all day. Reasons for optimism were rare: occasionally Smith edged, but his soft hands always ensured the ball dropped short of the slips, and an lbw review from England against Smith found that Anderson had over-stepped, although in any case the umpire's on-field call of not-out would have been upheld by the ball tracking.
No matter what Joe Root tried, it failed. In the morning, Smith brought up the fastest century of his Test career, a 138-ball effort that showed just as much ability to read the circumstances as had his slowest Test hundred, scored at the Gabba earlier in this series. He continued to be strong when cover-driving, when walking across the stumps and whipping to leg, and frankly playing wherever he wanted to.
Marsh was especially powerful driving straight down the ground and through the off side, and also found the gaps when cutting. He let out a roar after bringing up his home-town hundred in the final over before tea, with a pair of boundaries through point off Broad, the milestone coming from his 130th delivery. His efforts had continued a fine summer of selections from the Australian panel, who have found excellent contributions from Shaun Marsh, Tim Paine and now Mitchell Marsh, three selections that sparked much debate.
And still the runs kept piling up. Late in the day, Smith moved past his previous highest Test score of 215, and had been at the crease for nearly 10 hours. He was just the fifth Australia captain to score an Ashes double-century, after Billy Murdoch, Don Bradman, Bob Simpson and Allan Border.
Marsh by the close was eyeing off a double-century, a sentence which on its own tells all that need be told about this day. The result was that England were sunk, if not in the series, then at least in their hopes of winning this Test.
Brydon Coverdale is an assistant editor at ESPNcricinfo @brydoncoverdale