England captain Joe Rot endured his most difficult day in the job with the Australia pair flaying the tourists bowlers throughout a miserable day.
Despite starting the day 203-3, still trailing England’s first innings score by 200, the hosts ended it with a 146 runs lead with Smith unbeaten on 229 – his highest Test score – and Marsh 181 not out.
England need to win here in Perth to win the Ashes and while a draw would keep alive hopes they can retain them with victories in Melbourne and Sydney, that looked a distant hope at the end of day three.
With Australia set to resume in the morning with six wickets still in the tank, a huge first innings lead seems likely.
Given what is at stake there cannot have been a more dispiriting day in Root’s leadership of a Test side he took over in January for all that he will have known the feeling.
In India last winter, Root was part of Alastair Cook’s side which made 400 in Mumbai only to see the hosts post 631 then bowl them out for 195 to win by an innings.
And then in Chennai in the final Test England scored 477, India 759-9 declared then skittled Cook’s men for 207.
Something similar could be on the cards here after Smith and Marsh’s masterclass with the pair not giving England a single chance all day.
The solitary breakthrough, when Shaun Marsh edged to Root at slip for 28 off the bowling of Moeen, momentarily raised hopes at 248-4.
But his brother Mitch arrived and 300 runs later England had a mountain to climb.
There is rain forecast for today but probably not enough to significantly affect the result with a draw being the best England could hope for now.
For all that the two batsmen were in cruise control all day England were poor, summoning little in the way of energy and aggression and telegraphing plans with their bowlers in the way they set fields.
Four of England’s bowlers – Moeen, Stuart Broad, Chris Woakes, Craig Overton – were all hit for three figures. Only Jimmy Anderson kept his figures respectable but he finished wicketless.
Overton did well considering England revealed he has a hairline crack of a rib – most probably when he took a blow when batting against Josh Hazlewood in Adelaide.
The fast bowler apparently had a scan before play and before proving his fitness in the nets. However England confirmed he played with the aid of painkillers.