Australian teen sensation Alex de Minaur has emerged from a gruelling day on court to win his first ATP title, beating Andreas Seppi 7-5, 7-6 (7-5) in the Sydney International final.

Forced to win through his semi-final on Saturday afternoon against Gilles Simon after rain washed out play on Friday night, de Minaur returned to the court six hours later for a gutsy straight-sets win over the Italian veteran.

Broken in the first game of the opening set, it proved to be one of the few blights on the 19-year-old's game as he broke back five games and barely gave Seppi another look in.

In doing so, he became the youngest winner of the Sydney International since Lleyton Hewitt in 2001, and the first home talent to claim the prize since Bernard Tomic in 2013.

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It was also fitting he joined Hewitt as a 19-year-old winner, given there was so much about the Australian Davis Cup team captain — who again sat in his players' box with son Cruz — in the victory.

The world number 29's court coverage was immense as always, regularly chasing down his Italian opponent's forehands and wearing the 34-year-old down over the two hour, five minute clash to make amends for last year's final loss to Daniil Medvedev.

He also showed no sign of nerves, getting 73 per cent of his first serves in and bouncing back immediately after being broken midway through the second set and then three times when the world number 37 had mini breaks in the tiebreaker.

"It's crazy that this actually happened," de Minaur said.

"I thought it wouldn't happen. Third time lucky, and you guys don't know how much it means to do it in front of all you guys, in front of my home."

Alex de Minaur is champion of Sydney, the youngest since Lleyton Hewitt. ( AP: David Moir )

It came after de Minaur's earlier 6-3, 6-2 victory over Simon, where he never really looked challenged despite temperatures of more than 30 degrees.

It also took his daily court time to more than three-and-a-half hours, two days out from his first-round Australian Open clash with Portugal's Pedro Sousa.

Meanwhile, it was a disappointing end to the week for Seppi, who was playing in his first tour final in three-and-a-half years.

So close for impressive Barty

Earlier, Ashleigh Barty's dreams of a maiden home title have been crushed by Petra Kvitova in the Sydney International, beaten in a three-set epic 1-6, 7-5, 7-6 (7-3).

Petra Kvitova prevailed over Australia's Ash Barty in a three-set final of the Sydney International. ( AP: David Moir )

After Barty shot out of the blocks in the first set and led the deciding set 3-0, world number eight Kvitova fought back time and time again in the two hour, 19 minute classic while battling fatigue to claim her second Sydney crown.

Forced to serve to stay in the match at the end of the second set, Czech number five seed Kvitova fought back to break Barty for the first time to take the set and send it to a decider.

Both women broke each other three times in the third set, including back-to-back efforts from Barty as Kvitova served for the championship twice.

Kvitova's experience finally paid off as she powered home in the tiebreaker to claim her 26th WTA tour victory.

In turn, it also handed Barty her second straight runner-up finish in Sydney, after losing to Angelique Kerber in last year's final.

"I left everything out here and it wasn't quite enough," Barty said.

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Regardless, it showed world number 15 Barty is ready to challenge anyone at next week's Australian Open.

She beat world number one Simona Halep, number nine Kiki Bertens and number 12 Elise Mertens on her way to the final.

Kvitova apologised to Barty and the Sydney crowd for spoiling the Australian's Sydney party.

"Not to win at home, I'm sorry," Kvitova said.

"You know, one day you're going to make it for sure."

AAP