Serena Williams of the United States returns the ball during her women's singles final match against Maria Sharapova of Russia at the Australian Open tennis championship in Melbourne, Australia, January 31, 2015. Williams won 2-0. Photo:Xinhua

Illness, nor second-ranked Maria Sharapova, could stop the unyielding titan of women's tennis, Serena Williams, from getting her hands on her 19th Grand Slam after a straight-set win in the Australian Open final on Saturday.

A weary Williams fought off a chest infection and a fast-finishing Sharapova but maintained the upper-hand to take her sixth Australian Open 6-3, 7-6 (7-5) in one hour and 51 minutes.

In fitting style, the big serving American belted an unreachable ace and leapt with joy to repeat her 2003, 2005, 2007, 2009 and 2010 efforts at Melbourne Park.

Only Margaret Court on 24 titles and Steffi Graf with 22 Grand Slams are ahead of the American powerhouse, and while the 33-year-old dismissed with a shake of her head her chances of reaching those heights, she showed there is daylight between her and the rest of the world.

Williams had not lost against Sharapova since 2004 but, with her chest and throat reported to be worsening, many believed it was Sharapova's chance to finally break the 15-match streak.

As a sign of her afflictions, a spluttering Williams returned from a short rain delay early in the match only to again retreat off-court to vomit.

But the sickness only sharpened Williams' willingness to go blast the Russian off the court.

With cool nerves, she served rockets with pinpoint accuracy to ensure Sharapova had few look-ins to break ahead, while blasting 38 winners in total.

As the final stretched into a second hour, Sharapova's stocks rose and the lengthening rallies wore out the American.

However, Williams aced herself out of tight spots time-and-again to heap pressure back on the wayward Sharapova serve.

The world No.1 later told a packed press conference she had felt unwell throughout the tournament's second week.

"I've been through so much the past week (that) I really, really didn't expect to win," said Williams.

"Every time I didn't feel great, I started to feel better, and then the next day I got worse. There were a lot of ups and downs. It's been a long time since I've been to the final here or the semi-final."

In the first championship playoff between the top two seeds since 2004, Williams said she was honored to have beaten the world No. 2 in the high-class display.

"She gave us a great final not just for (the fans) but for women's tennis," Williams said.

The world No. 1 began her sixth Australian Open final perfectly, grabbing the ascendancy with a break in the first game.

Just as she did throughout the match, Williams took Sharapova's erratic second serve from a foot inside the baseline and blasted winners.

Such was her dominance on the world No. 2's serve in the first set that Williams broke twice in a row to love.

Sharapova showed better resistance in the second set but she was unable to produce more than a solitary break point.

Sharapova twice got to 0-30 on the world No. 1's serve but could only watch on as the ruthless American fired consecutive unreturnable serves to dig her way out.

"I didn't feel I had many chances to get in the point," said a despondent Sharapova.

"As much as I would love to hit a 200-kilometer-an-hour serve, I just don't think it is feasible with my shoulder."

Sharapova defended a championship point in the tenth game with a clutch forehand she has trademarked as her own.

It was one of the few times that the dominant Williams was forced to sprint along the baseline.

Its infrequency displayed the gulf between the women ranked one and two in the world.

In the second-set tiebreak, Sharapova's early mini-break, earned with a bold forehand return, quickly evaporated when her serve faltered.

"In the tiebreaker, I gave her many looks on the second serve," said the No.2 seed.

"Even though they were good, deep second serves, she was ready. Aggressive."

It allowed the powerful Williams to push the Russian deep and move to a 4-1 lead that Sharapova could never fully draw back.

Williams departs Melbourne having matched her United States Open haul of six championships.

She has also won twice at the French Open and five times at Wimbledon.