MELBOURNE, Australia -- Second-ranked Dinara Safina retired while she was down 4-5 at the Australian Open on Sunday, serving at 30-40 in the first set of her fourth-round match against Maria Kirilenko, who had ousted 2008 champion and fellow Russian Maria Sharapova in the first round.
While the seeded players dropped, former No. 1 Justine Henin continued her run in her first Grand Slam tournament in two years with a 7-6 (3), 1-6, 6-3 win over fellow Belgian Yanina Wickmayer, keeping her on track for a quarterfinal meeting with Petrova.
Safina, the 2009 Australian finalist who held the No. 1 ranking despite never winning a major, limped off when facing set point against Kirilenko when a back problem flared up.
"It was getting worse and worse, I have no idea how it happened. It was really terrible," said Safina, who saw her season last year end prematurely because of a back problem. "I turned to my coach and I said I cannot move anymore. It's shocking."
Petrova compared her wins over Clijsters and French Open champion Kuznetsova.
"Today was similar. I felt like my motivation, my concentration was on the same level," Petrova said.
The 27-year-old Russian doesn't think she's reached her potential yet -- her best runs in the majors finishing in semifinal losses.
"I know there's still a lot to accomplish," Petrova said. "That's what I'm really looking for."
Henin, who is unranked and playing on a wild-card entry in her second tournament since returning from a 20-month retirement, told the crowd she'd missed tennis too much to resist a comeback.
"It's been a great moment for myself," Henin said. "It's a great feeling to be back, been a great fight, and thank you."
The seven-time Grand Slam winner dominated the first-set tiebreaker after saving three set points in the 12th game. After dropping the second set, Henin broke Wickmayer's serve to open the deciding third set and was on top after that.
In an afternoon match, 2008 Wimbledon semifinalist Zheng Jie set another national mark by becoming the first Chinese player to reach the quarterfinals at Melbourne Park with a 7-6 (6), 6-4 victory over Alona Bondarenko. She next plays Kirilenko.
"I think Australia is lucky for me because I win the first Grand Slam doubles title in Australia," said Zheng, who won the Australian Open and Wimbledon doubles titles in 2006 with Yan Zi. "So I'm so happy I'm in the quarterfinal of Australia also."
She and No. 16 Li Na both reached the fourth round here, the first time two Chinese players have reached that stage at the same Grand Slam tournament. With one on each half of the draw, Zheng said they can both go further.
"But I think we can go the far way," she said. "I hope we can be in the semifinal for both Chinese players, yes."
Bondarenko, seeded No. 31, had been on an eight-match winning streak after a title run at Hobart last week, which included a quarterfinal win over Zheng.