A fired-up Serena Williams bludgeoned her way into the Australian Open semi-finals with a nailbiting 3-6, 6-2, 8-6 win over Israeli 16th seed Shahar Peer on Tuesday.

Williams came within two points of defeat before reaching the last four at Melbourne Park for the third time and ominously for her rivals, the American has gone on to win the title each time she has made it this far.

"I'm the ultimate competitor," she told the Rod Laver Arena crowd. "I love to compete, I always have even if I'm playing cards or signing autographs the quickest."

After an injury-wrecked 2006, world number 81 Williams was the lowest ranked player to reach the quarter-finals.

Peer, showing the toughness one would expect from someone who started mandatory army training in 2005, bossed the match in the early stages but Williams looked the only winner at the death.

The seven-times Grand Slam champion has lived up to her billing as a dangerous floater with Peer becoming the fourth seed to fall prey to the Williams onslaught.

Peer, aiming to become the first player from her country to reach a Grand Slam singles semi-final, looked to be heading out at 4-1 down in the final set but she refused to crumble.

The 19-year-old levelled at 4-4 after her fizzing forehand passing shot whizzed past a lunging Williams and rattled the American further by breaking for a 6-5 lead.

Peer served for the match in the next game but was undone by her lack of self-belief as Williams pumped herself up to stay alive.

The former world number one appeared to find inspiration from the notes she read during changeovers and after two hours and 34 minutes of enthralling action on a baking Rod Laver Arena, Peer surrendered by floating a backhand wide.

Williams greeted her moment of glory by jumping up and down the court before holding aloft her index finger to the crowd as if to say "I'm still number one".

She now faces another formidable opponent in the last four after Nicole Vaidisova triumphed in the battle of the Czech teenagers.

The 10th seed lies in wait for Williams after the mature 17-year-old waltzed past fellow Czech Lucie Safarova 6-1 6-4 to reach her second career Grand Slam semis.

It took just 71 minutes for her to beat the conqueror of defending champion Amelie Mauresmo, and she now faces her stiffest test against the improving American.

Another success story from coach Nick Bollettieri's production line in Florida, Vaidisova was clearly impressed by one trait she picked up there -- single-mindedness.

"Everywhere I go I have a Czech mind. It's not like when I got to Asia I try to change to my Asia mind, then use my Australia mind. I'm definitely influenced by America, but still keeping my one Czech mind."