Serena Williams planned to celebrate her 19th grand slam title by heading to bed after defying illness and a battling performance from Maria Sharapova to win the Australian Open on Saturday.

Williams fired 15 aces in the second set to extend her winning streak against Sharapova to 16 matches with a hard-fought 6-3 7-6 (7/5) victory in an hour and 51 minutes on Rod Laver Arena.

The 33-year-old revealed she had been sick off court during a rain delay in the opening set but recovered to move closer to the open-era record of 22 grand slam titles held by Steffi Graf.

Williams had been tied with Chris Evert and Martina Navratilova on 18 after winning the US Open last year and Navratilova was on hand to present the trophy after Williams claimed her sixth Australian Open title and first since 2010.

Sharapova, whose last win against Williams came in November 2004, got off to the worst possible start by serving a double fault to lose her serve in the opening game.

Williams led 3-2 and was serving at 30-30 when rain forced the retractable roof to be fully closed, leading to a 12-minute delay.

Sharapova remained in her chair but Williams left the court and later revealed on Channel 7: "I had a really bad cough and ended up throwing up actually. I think that helped when I got everything out of me and cleared my chest out because I couldn't breathe a little bit.

"I've had a really bad cold and cough. Usually when that happens you stay in bed for a week, you don't play matches every other day and practice every other day. Now I have a couple of days to take a deep breath and lay down.

"I'm going to go to bed and curl up under some covers and go to sleep. That sounds excellent right now."

Speaking during the trophy presentation, Williams said: "Growing up I wasn't the richest but I had a rich family in spirit and support. Standing here with 19 championships is something I never thought would happen. I just can't believe it, I really can't.

"I went on the court (in Compton, Los Angeles) with just a ball, a racket and a hope and that's all I had."

Sharapova, who saved two match points in the second round against Alexandra Panova, said: "I have to congratulate Serena on creating history and playing some of her best tennis.

"It's an honour playing against her. I've not beaten her in a really long time but I love stepping on the court every time because she has been the best and you always want to play the best.

"I was almost down and out in the second round so feel I gave myself a second life in this tournament. It was not quite enough today but I am proud of my effort.

"It's always tough getting to a final stage of an event and you become the one that's going home with the smaller trophy. No matter how you played, well or not, whatever the scoreline is, it's always tough. But it will be all right.

"Yes, I haven't won against her many times, but if I'm getting to the stage of competing against someone like Serena, I'm doing something well. I'm setting up a chance to try to beat her and it hasn't happened. I'm not just going to go home without giving it another chance. That's just not who I am and not who I was raised to be. I'm a competitor."

Williams returned following the delay to immediately serve an ace and hit a forehand winner to hold, before making it six points in succession to claim a second break. And although she promptly lost her own serve, she responded by breaking Sharapova for a third time to take the set in 47 minutes.

Sharapova had to come up with some impressive serves, including two aces, to save two break points at the start of the second set, but Williams was not to be outdone in the serving stakes.

The American hammered down 11 aces in four service games and shrugged off the loss of a point for prematurely celebrating what she thought was another, Sharapova somehow getting a backhand return back into court as Williams shouted 'Come on'.

That "hindrance" call led to a break point for Sharapova in the seventh game but Williams accepted it without question and went on to hold serve to keep her nose in front.

Serving second, Sharapova was under intense pressure in each service game and had to save a match point at 4-5, producing a forehand winner right into the corner that even had her opponent applauding.

A tie-break was required to decide the outcome and Williams thought she had served an ace to win it only for a let to be called, but after a rueful smile she thumped down her 18th ace of the match to seal victory.

Williams admitted she would like to equal Graf's record tally, but knows she will have a battle on her hands with the likes of 20-year-old Eugenie Bouchard and 19-year-old Madison Keys already challenging for grand slam titles.

"I would love to get to 22," Williams said. "I mean, 19 was very difficult to get to. Took me 33 years to get here. I would love to get there but I have to get to 20 first, and then I have to get to 21.

"There's so many wonderful young players coming up, so it will be a very big task. My next goal was just to get to 19. I didn't think it would happen this fast, to be honest, but it feels really good."