By Miles Evans

Serena Williams needed every ounce of her competitive spirit to prevent Shahar Peer from crashing her Australian Open comeback party on Tuesday.

Peer, 19, was already in uncharted territory for an Israeli woman by reaching the last eight of a slam and she had one foot in the semi-finals until the seven-times major winner shut the door in her face after three tight sets.

Meanwhile sixth seed Andy Roddick showed there was no mercy when playing your friends as he hammered fellow American Mardy Fish to book his third semi-final place at Melbourne Park.

Unseeded Serena, champion in 2003 and 2005, won 3-6 6-2 8-6 in two hours and 34 minutes after Peer had come within two points of victory.

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.

ULTIMATE COMPETITOR

"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."

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 semi.

It took just 71 minutes for her to beat the conqueror of champion Amelie Mauresmo, but 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 go 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," she said.

As a bleary-eyed Melbourne Park recovered from the epic Rafael Nadal v Andy Murray clash that finished at 0151am local time on Tuesday, it was left to Roddick to provide the pick-me-up in the men's draw.

PLAN 'A'

After coming through a five-setter against Mario Ancic, it was back to plan 'A' as Roddick tore apart unseeded Fish in three one-sided sets.

Fish had gone into the match rejuvenated by earlier wins over fourth seed Ivan Ljubicic and 16th seed David Ferrer, but Roddick served and blasted his way into the last four after just 87 minutes on Rod Laver Arena.

The American immediately had his next match in mind the moment he walked off the court.

"I'd like to play Roger (Federer in the semi)," said Roddick after the 6-2 6-2 6-2 victory.

"I've lost to him a bunch of times and he's a great player but I feel like I'm improving a lot right now, I'd love to play him."

Only Tommy Robredo's closest confidantes would consider the seventh seeded Spaniard as anything other than roadkill on Federer's inexorable journey to a third Australian Open title.

Robredo won their first meeting at the 2002 Hopman Cup but it has been one-way traffic since with the Swiss maestro crushing the Catalan six times for the loss of just one set.

They play in the evening session's standout match.