MELBOURNE, Australia - Serena Williams answered her critics with an overpowering victory in the Australian Open final.

Unseeded and ranked 81st, Williams won for her eighth and most improbable Grand Slam title Saturday, beating Maria Sharapova 6-1, 6-2.

“It was an awesome win, because I had so many critics. So many people ... saying negative things,” Williams said. “Saying I wasn’t fit, when I felt that I was really fit, and I could last three sets.

“It’s always like, tell me no and I’ll show you that I can do it. I get the greatest satisfaction just holding up the Grand Slam trophy and proving everyone wrong.”

Only the second unseeded woman to win the Australian title in the Open era, Williams came to Melbourne Park with only three matches at a low-key warmup tournament after missing most of last season because of a knee injury.

She will jump to No. 14 in the world next week after capturing her first title in 15 tournaments since her second Australian Open victory in 2005.

Despite doubts about her fitness, Williams thought she was in great shape.

“I have been working really hard and haven’t felt like my results have been showing,” she said. “And finally it just all came together, especially in the final match.”

The victory was the most dominating win in a completed championship match at Melbourne Park since Steffi Graf beat Arantxa Sanchez-Vicario 6-0, 6-2 in 1994.

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“This definitely goes down as one of my good matches. I’m insatiable,” Williams said. “I think I could have done better. That’s just my character.”

She finished off the top-seeded Sharapova with a backhand winner, then threw her racket in the air and dropped onto her back on the court.

The 25-year-old American, also the 2003 champion, got up and skipped over to the side of the court, swapping high-fives with mother Oracene Price and other people in the stands before jogging back onto court with her arms up in triumph.

Williams dedicated the title to her half-sister, Yetunde Price, who was killed in a 2003 shooting.

Mark Dadswell / Getty Images Maria Sharapova suffered her worst loss in a Grand Slam event, but will still take over the No. 1 ranking from Justin Henin.

“Most of all I would like to dedicate this win to my sister, who’s not here. Her name is Yetunde. I just love her so much,” she said, her voice cracking. “I’ll try not to get teary-eyed but I said a couple of days ago, if I win this it’s going to be for her. So thanks Tunde.”

Chris O’Neill, who was ranked No. 111 when she won the 1978 title, was the only other unseeded woman to win the Australian Open.

Sharapova had no answers for Williams’ power in her worst loss in a Grand Slam event.

“You can never underestimate her as a performer. ... I know what she’s capable of and she showed that today,” said Sharapova, who will assume the No. 1 ranking from Justine Henin. “She has showed it many, many times.

Williams saved match points in her semifinal win over Sharapova here two years ago before beating Lindsay Davenport in the final.

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She started aggressively and never relented in the kind of form that helped her dominate women’s tennis as she completed the “Serena Slam” with four consecutive majors up to the 2003 Australian Open.

She held to open and then won 12 straight points after Sharapova had a game point in the next to jump to a 4-0 lead. Williams saved a break point in the fifth game before Sharapova held at love to make it 5-1.

Williams served out, taking the first set in 26 minutes on her second set point when Sharapova sent a backhand service return wide.

The American broke Sharapova’s serve and resolve again to open the second set, then had consecutive double-faults to give the 19-year-old Russian a break point chance in the next game. In a manner typical of her determined performance Saturday, Williams fired an ace to save the break point and held on back-to-back errors by Sharapova.