Caroline Wozniacki dragged herself back from the brink to power into the semi-finals of the Australian Open with a gritty 3-6, 6-3, 6-3 win over a dogged Francesca Schiavone on Tuesday.

Down a set and trailing 3-1, the Danish top seed shifted up a gear and burned through the next five games, sealing the second set when the Italian pushed a weak return down the tram-lines at Rod Laver Arena.

The 30-year-old Schiavone battled hard in the third, but the strain of her record-breaking marathon against Russia's Svetlana Kuznetsova appeared to show as she gifted her opponent easy points with a raft of sprayed volleys and miscued drop-shots.

The feisty Italian saved three match points and broke back to trail 5-3, but surrendered after 144 minutes on a fourth match point when her backhand flew just wide.

Wozniacki will play China's Li Na for a place in the final.

Roger Federer flattened his close buddy Stanislas Wawrinka 6-1, 6-3, 6-3 to move menacingly into the semi-finals on Tuesday, showing scant regard for sentimentality.

Defending champion Federer, the Melbourne second seed, brought a ruthlessly swift end to the first grand slam quarter-final contested by two Swiss men in an hour and 47 minutes.

"I prefer to play aggressive," Federer told reporters,

"I think at crucial times it haunted me playing a bit passive instead of trying to take it to the opponent a bit more. With success sometimes you get a bit comfortable. Because it's working, why change it?

"I was always trying to look for new ways but there were times it didn't work against a few players, or I ran into a few players at the wrong times maybe."

Federer, who suffered a lean spell at the grand slams after winning in Melbourne last year, credited Pete Sampras's former coach Paul Annacone for helping him rediscover his magic touch since teaming up last July.

The resurgent Swiss, winner of the 2010 World Tour Finals and in Doha in the run-up to the Australian Open, blew Wawrinka off court in a blur of winners.

"I seem to have the right game plan," said the 16-times grand slam champion after extending his winning streak to 15 matches and reaching his eighth consecutive Melbourne semi-final.

"Obviously with the many wins I've had in the last four or five months, it's been much easier."

Federer won a doubles gold medal alongside Wawrinka at the 2008 Beijing Olympics but his eighth win in nine meetings with the man he fondly calls "Stanli" was cruelly lop-sided.

Li Na stormed into her second successive Australian Open semi-final with an impressive 6-2, 6-4 victory on Tuesday that left vanquished opponent Andrea Petkovic tipping her to win China's first singles grand slam at Melbourne Park.

Li, her country's first top-10 player, was broken in the first game of each set but recovered brilliantly with a clinic of clean hitting to bully the German off the baseline and wrap up victory in 80 minutes.

"I think she's going to win the tournament," said 30th-seeded Petkovic, who struggled in the sun at Rod Laver Arena after playing evening sessions in earlier matches.

"It's nothing that I can tell you, (whether) her forehand is good or her backhand. It's just the feeling, how she is on court, her confidence and the way she's playing.

"Sometimes you get the feeling during the match that somebody is really strong and just has that confidence going on, that aura maybe."

The 28-year-old Li has not conceded a set in her five matches at the tournament and will bid for a place in the final against top seed Caroline Wozniacki or Francesca Schiavone.

She carries a 10-match winning streak into the contest after winning the warm-up Sydney International title where she upset finalist Kim Clijsters, a likely opponent in the final at Rod Laver Arena.

Ominously for the women ahead of her in the draw, confidence player Li said she was enjoying her tennis more than last year, when she went down fighting to eventual champion Serena Williams.

"I think (I) was the same (as last year). But right now (I'm) feeling more happy on the court," said Li, who, with countrywoman Zheng Jie, became China's first singles grand slam semi-finalists last year.

A chest-thumping Novak Djokovic blasted his way past Czech Tomas Berdych 6-1 7-6 6-1 in a heavyweight clash on Tuesday to set up an Australian Open semi-final with Roger Federer.

"I have nothing to lose against Federer," Djokovic told reporters. "He's the title holder and we all know how good he is. He's the best player ever.

"I have to be confident and stay positive," added Djokovic, who knocked the Swiss maestro out of last year's U.S. Open at the semi-final stage having saved two match points. "If I play well I have a chance."

The Serb third seed, Melbourne champion in 2008, caught fire early, tearing through a one-sided first set in just 36 minutes under floodlights at Rod Laver Arena.

Sixth seed Berdych dug deep to force a tiebreak in the second but a wild forehand from last year's beaten Wimbledon finalist gifted it to Djokovic 7-5, and with it a two-set lead.

Berdych, cheered on again by an army of bare-chested Australian fans, hung his head, knowing he needed a minor miracle to turn the match around.

Djokovic quickly went for the jugular in the third, securing a double-break for 5-1 with a drilled forehand return and finishing off Berdych with a big serve down the middle after two hours and 32 minutes.

"I didn't even have two weeks off after winning the Davis Cup with Serbia," said Djokovic. "But I've played some of my best tennis in the last couple of months."