Jason Gillespie produced the unthinkable as Australia steamrolled its way towards an inevitable series whitewash over Bangladesh.

Gillespie (201no) handed himself the most unlikely 31st birthday present by becoming the first nightwatchman to score a double century in the second Test at Chittagong Divisional Stadium.

The tailender and Mike Hussey (182) trashed the feeble Bangladesh attack in a 320-run fourth wicket stand on day four as Australia made 4(dec)-581, the highest Test total recorded against the minnow.

Bangladesh was sliding to a hefty defeat at 4-195 in its second innings, still needing another 189 runs to make the tourists bat again, with Shahriar Nafees (75no) and Aftab Ahmed (1no) unbeaten.

But it was Gillespie, who averaged 15.69 before the match, who provided the headline act for the second straight day and again overshadowed Hussey's exhilarating knock.

He enjoyed overhauling the best scores of his fast bowling teammates but had bigger fish to fry.

"He told me every Test or former Test players' highest score that he passed he ticked them off, he knew them all," Hussey said.

"When he passed Mark Waugh (153no) he ticked him off, he went past Michael Clarke (151) and then Steve Waugh (200).

"And Boony (200)" Gillespie chirped in.

Gillespie was in wonderland over his knock.

"This is unbelievable it is a fairytale it is Hansel and Gretel and Dizzy's double hundred it is one in the same ... an absolute fairytale," he said.

"This is ridiculous two days in a row to be talking about my batting."

He again made making runs in Tests sound like a simple exercise.

"I was lucky, a few shots came off, had a bit of luck, pretty much the same as yesterday," he said.

Hussey praised his batting partner for his powers of endurance.

"I think it is a real testament to his concentration to be able to bat for so long especially as not being a recognised batsman," he said.

The paceman joined Wasim Akram as the only cricketers to have taken 250 Test wickets and scored a double century.

The South Australian returned to the crease on Wednesday on 102 but managed to craft out another 99 runs in blistering fashion by his standards.

His epic nine-and-a-half-hour knock came off 425 balls and he struck 26 fours and a pair of sixes.

Gillespie leg-glanced spinner Mohammad Rafique to the boundary to register his double ton and after realising the ball had gone to the fence he charged towards the dressing room to acknowledge his teammates.

He ripped off his helmet, bowed to his teammates and shook his head in disbelief and muttered some expletives to boot about his surprising achievement.

Australia immediately closed its innings but there was little time for rest and 10 minutes later the paceman was limbering up on the field in readiness to bowl the second over of Bangladesh's second dig.

But just when Gillespie felt that everything was going his way, first slip Shane Warne (3-63) dropped a straightforward chance off his bowling with Bashar on zero.

Warne more than made up for his error by dismissing Habibul Bashar (49), Rajin Saleh (5) and Mohammad Ashraful (29) late in the day after Brett Lee removed opener Javed Omar (19).

Gillespie and Hussey earlier recorded Australia's third highest fourth wicket stand and Gillespie branched out from his normal defensive role by hitting two sixes and upping the tempo.

He lofted a straight six off Abdur Razzak and then smacked part-timer Saleh over the midwicket fence to show another side to his game.

The ease with which he tallied the runs made it difficult to believe he had only made two half centuries in 70 Tests before this week.

However he was assisted by a Bangladesh attack that struggled on a good batting track.

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