Two moments of madness set up final-day epic at the SCG after Jacob Bethell's maiden Test century

SCG: During England's first innings, the cricketing fraternity thought they saw the dumbest shot ever from Jamie Smith.

Then Will Jacks walked in at 5-219 on day four at the SCG and said hold my drink.

With Jacob Bethell passing 100 at the other end, Jacks decided he'd try to hit a six with his second ball and was instead caught by Cameron Green at deep mid-wicket.

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It was a shot that beggared belief and summed up England's series as a whole.

Immature, ridiculous and reckless.

"I can't believe the shot I've just seen," Michael Vaughan said on Fox Cricket.

Jacks' shot gifted Beau Webster his second wicket having removed Harry Brook for 42 two balls before from a successful lbw review.

Brook was also trying his best to get out the over after Bethell had passed his ton.

The right-hander was playing reckless shots against Mitchell Starc and then didn't play for spin from Webster.

The two wickets meant England went from a position of control at 3-219 to 5-219.

Both dismissals still didn't take away from Bethell's masterclass.

While Jacks was reckless, the wunderkind was the opposite.

Everything about his maiden Test century was mature, elegant and technically sound.

"A star is born at the SCG," Michael Vaughan said on Fox Cricket after Bethell brought up his ton.

Australia started the day with a lead of 134 and three wickets in hand. England had cause for concern when Ben Stokes departed early, failing to finish his over due to an adductor injury.

Steve Smith couldn't make the most of his departure, falling again to Josh Tongue for 138. The tail didn't wag as Mitchell Starc (5) became another Tongue victim while Scott Boland was gone for a golden duck, caught at slip by Harry Brook off Will Jacks.

Australia finished all out for 567, leading by 183 runs.

England's second innings was off to a horror start again when Zak Crawley left alone a Mitch Starc delivery and was hit on the pads, making it 1-4.

Ben Duckett once again failed to make the most of a start, chopping on off Michael Neser for 42.

Joe Root (6) was the next man gone, given out lbw off Scott Boland at 3-117.

Bethell and Brook then combined for a 102-run partnership before the collapse came.

Then Jamie Smith and Bethell looked like they'd brought calm.

That was until Bethell hooked Marnus Labuschagne around the corner. He and Smith then had a mix-up with the latter run out for 26.

"Absolute chaos at the SCG - a calamitous error," Isa Guha said.

Stokes came out after him and hobbled around the crease before edging Webster to Steve Smith for 1 off just five deliveries.

Brydon Carse (16) was next to go with Smith taking another catch, this time from Boland's bowling.

Bethell then took it upon himself to hog the strike with Matthew Potts at the other end. Both men finished unbeaten at stumps with Bethell on 142 and Potts 0.

England's total at the end of day four is 8-302 with a lead of 119 runs.