Root 42*, Bairstow 17*
Two wickets for Lyon
Aus 649-7 dec - lead of 303
S Marsh 156, M Marsh 101
Moeen 2-170, Crane 1-193
Australia lead five-Test series 3-0
Day five starts at 23:30 GMT
Trail by 218
Shot! Width from Josh Hazlewood and too full as he tries a slower ball, and Jonny Bairstow bends his back leg and drives him to the cover boundary. The inevitable bumper comes Bairstow's way in response, and he tucks himself underneath it.
Ebony Rainford-Brent
Ex-England batter on BBC Test Match Special
I've been saying for a few Tests that there is not much between these two teams. But after today, I think the gap is actually wider than we've perceived for a while.
Smith's best Test wicket haul is 3-18. He's also got Jonny Bairstow out once before, back at Lord's in 2013.
He tosses one up invitingly but Bairstow whirls his wrists and clubs a single safely away. Joe Root gets forward and smothers the spin, keeping his pad safely out of the way.
Steve Smith is bringing himself on! That ends Lyon's spell of 17-4-31-2.
Simon Mann
BBC Test Match Special commentator
Joe Root is playing really well here. It's as if he is saying, "over my dead body".
Joe Root gets up on his toes and cracks a shot away through the off side, but there's a cannily placed fielder there and he cuts off the ball. Steve Smith at slip is furiously whirring his arms around. Is he going to give himself a bowl?
Josh Hazlewood then cuts Root in half with a delivery not dissimilar to the one that dismissed Mitch Marsh earlier. Root readjusts and gets in line behind the ball, and plays out a maiden.
Andrew Samson
BBC Test Match Special statistician
Nathan Lyon has bowled 241 overs in this series - more than anyone else.
Trail by 223
Joe Root dinks a single away behind point, before Nathan Lyon mixes up his speeds to Jonny Bairstow. Some sharp turn surprises Tim Paine, who moves across to collect the ball and ends up getting a surprise rap on the gloves.
That boundary from Bairstow in the last over was only the second of the innings. Joe Root hasn't struck one yet - he's on 37 from 98 deliveries.
Glenn McGrath
Ex-Australia pace bowler on BBC Test Match Special
Steve Smith has been able to bowl Nathan Lyon continuously and rotate the seamers. England had to get on top of Lyon to have a chance in this series. At no stage have they been able to do that.
Simon Mann
BBC Test Match Special commentator
Australia's bowlers have hunted as a quartet in this series. It has been mightily impressive.
Four! That's the first boundary for Jonny Bairstow but it's not entirely convincing. It's wide from Josh Hazlewood and Bairstow throws his arms at it, and a thick outside edge rolls through gully and away for four. Hard hands.
Bairstow then leaves a delivery that nips back and, somehow, rises over the top of his stumps. Meanwhile, down on the boundary, Pat Cummins is being mobbed by autograph hunters.
Simon Mann
BBC Test Match Special commentator
Teams that have been four wickets down going into the final day have saved Test matches before - famously England against South Africa in Johannesburg in the mid-nineties - but no team has saved one from five down overnight.
Another switch of seamers for Australia. Josh Hazlewood replaces Mitch Starc.
Andrew Samson
BBC Test Match Special statistician
On three occasions four bowlers have taken 20+ wickets for a team in a Test series:
Bairstow 4, Root 36
I imagine Steve Smith is a rather intense fella. He's got an interesting array of facial expressions.
Joe Root drops and meanders through for a single, before Jonny Bairstow plays a horrid, uppish drive. The ball hangs in the air but there's no fielder close enough, Bairstow calls Root through for a single, and his mate has to stretch and push his bat over the line to get home. Bairstow taps his helmet afterwards, reminding himself to stay alert.
Dan Norcross
BBC Test Match Special
What is nice is that now Nathan Lyon is bowling to two right-handers, we can expect at least 85 runs before his next wicket.
Trail by 233
Jonny Bairstow's face is slathered in suncream. He's off the mark as Mitch Starc fires down a slightly leggy delivery, and he clips it off his hips for a single.
England are grimly trying to save the game and avoid a 4-0 series defeat at the SCG.
Australia finally declared on 649-7 about an hour before tea, leading by 303 runs.
In reply, Mark Stoneman was trapped lbw by Mitch Starc for a duck, before Nathan Lyon bowled Alastair Cook, leaving England reeling on 15-2.
James Vince got through to tea but then got out...well, you know how. Yet again the number three nicked off while driving, caught at slip for 18. Dawid Malan has just departed lbw to Lyon, playing late to one that skidded on.
Earlier, Shaun Marsh duly reached his second century of the series, turning it into a 150 before he was run out. He celebrated with young brother Mitch, who then did the same as he reached his second ton of this Ashes - the Marsh duo putting on 169 to grind England down on a blisteringly hot day in Sydney.
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