MELBOURNE: Roger Federer and Serena Williams showed championship form to battle back from a set down and storm into their semi-finals at the Australian Open here today.

Li Na also made the last four with an upset victory over Venus Williams, giving China two players in a Grand Slam semi for the first time. Her reward is a clash with top seed Serena.

But the tournament ended for ailing third seed Novak Djokovic who was knocked out in a thrilling five-setter by 10th seed Jo-Wilfried Tsonga, the man he beat in the 2008 final. The Frenchman will now meet Federer, who was given a scare by sixth seed Nikolay Davydenko when the Russian led 6-2, 3-1 before the Swiss star clicked into gear.

He won 13 straight games to take the next two sets before a titantic struggle in the fourth with the 15-time Grand Slam champion eventually coming home 2-6, 6-3, 6-0, 7-5 to end Davydenko’s 13-match winning streak. It puts Federer into his 23rd consecutive Grand Slam semi-final, having never missed out since his third round defeat to Brazilian Gustavo Kuerten at Roland Garros in 2004.

“I’ve played him many times and I know he goes through phases for half an hour, an hour,” Federer said of Davydenko. “You’ve just got to stick with him and if you don’t he’s going to crush you. All of a sudden I went on a run like I did and that was a bit surprising, but I needed that cushion at the end of the fourth when he played well.” Asked if he was concerned he might lose, he said: “I was a touch worried, let’s put it that way.”

Tsonga prevailed 7-6 (10/8), 6-7 (5/7), 1-6, 6-3, 6-1 in a near four-hour marathon against Djokovic, who was struggling with illness and at one point took a medical timeout for an upset stomach. It was sweet revenge for the Frenchman after his 2008 disappointment. “It was just amazing the level we played at. I’m so happy I won,” said Tsonga, who added he would be ready for Federer on Friday despite being taken to five sets in his past two matches — the only five-setters of his career. “I will be ready,” he said. “It’s going to be tough though, he’s the best player ever.” Fifth seeded Andy Murray faces 14th seeded Croat Marin Cilic in the other semi-final on Thursday, with the Scot seeking to win Britain’s first Grand Slam since Fred Perry in 1936.

Like Federer, Serena was also on the ropes before staging a comeback to stay on track for her fifth Australian title. She was down 4-6, 0-4 to seventh seed Victoria Azarenka before fighting back and winning a tense tiebreaker to level the match. Azarenka was rattled and Serena rammed home her advantage to win 4-6, 7-6 (7/4), 6-2 and set up a clash with Li, who came from behind to shock Venus 2-6, 7-6 (7/4), 7-5. Justine Henin and unseeded Chinese Zheng Jie contest Thursday’s other semi.

“I am surprised and I am just happy to still be here,” said Serena. “I didn’t expect to win when I was down 0-4.” Venus should have made it a sister act in the semis, but she threw it away against Li in a scrappy match where they made a incredible combined 110 unforced errors. She was a set and 4-2 up in the second when Li made her move, playing with greater freedom as Venus tightened up, with her forehand going t life,” an exuberant Li said.