MELBOURNE: American teenager Madison Keys said she was hungry for more Grand Slam success Thursday after a breakthrough Australian Open when she pushed top seed Serena Williams in the semi finals.

The big hitting 19 year-old has already been tipped as a future Grand Slam champion by Williams and lived up to the hype in a final four clash with the 18 time major winner that she lost 7-6 (7/5), 6-2 after saving eight match points.

"I'm really happy to have gotten this far in a tournament," she said  after becoming the only unseeded player to reach the semis.

"It's my first one. Just looking forward to having more.

Hopefully I'll have a couple where I'm with the trophy at the end of the week."

Venus Williams declared "the sky's the limit" for Keys after the teen beat her in a tight three set quarter final at Melbourne Park and Serena was equally impressed after their last four match.

"She's obviously a great player, she's going to be winning this tournament very soon and lots of other Grand Slams," said the younger Williams sister, who hugged Keys at the end of play.

Williams said it was a relief to see a new potential standard bearer for US tennis, as her and Venus are now both in their 30s, although she clarified her retirement was not imminent as she chases a 19th Slam.

"It great to see her do so well as an American," she said "Myself and my sister, we've been fighting so long. Now she's coming up.

"So many other Americans, as well. But her in particular, just doing so well consistently.

She just has this desire to be the best. That's what it takes."

Even Williams' opponent in the Australian Open decider, Russian second seed Maria Sharapova, said she had been monitoring the potential threat of Keys for some time.

"I've watched her for a few years now kind of rising up the rankings," the world number two said.

"And, yeah, I think this is her real breakthrough.

The potential she has is tremendous."

Keys, who is coached by former Grand Slam champion Lindsay Davenport, said her stirring run at Melbourne Park had showed her she could compete with the best at the majors.

"I can play the number one player in the world in a pretty close match," she said.

"So for me that's inspiration for every time I'm on a practice court to keep working, keep getting better so I can have more and more weeks like that."

Keys, whose ranking is set to break the top 20 after the tournament, also showed she was staying grounded when asked about statistics showing she had the fastest ground strokes of any player, male or female, currently on tour.

"The fact that it's coming off my racquet hard is nice, but I had that stat at the French Open and lost first round, so it doesn't really say much," she said.

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