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Samantha Stosur felt great before things started to spin out of control.

She was playing before her home crowd at the Australian Open and she was winning — by a lot. The anxiety that had risen so often on center court seemed at bay.

Up 5-2 in the third set, Stosur was two points — just two points — from reaching the third round.

"It was close to being a great day," Stosur said, trying to analyze what went wrong. "And now, it's not such a great day."

Her tenacious opponent, the 40th-ranked Zheng Jie of China, won the next five games and won 6-4, 1-6, 7-5. The match ended with one last double-fault from Stosur — she had nine in total and 56 unforced errors.

"Obviously it's a hard one to take when you get yourself into a winning position and you lose five games straight," she said. "It just kept happening, point after point after point."

Asked how much of her problem was mental, she replied, "A hundred percent."

Stosur reached the French Open final in 2010. She beat Serena Williams to win the U.S. Open in 2011, becoming the first Australian woman to earn a singles major title in more than 30 years.

But coming home brings on the jitters. In 13 appearances at the Australian Open she has never made it past the fourth round. In 2011 and 2012, she exited abruptly in the first round.

Just before heading to Melbourne this month, the ninth-ranked Stosur lost in her first matches of warm-up tournaments in Brisbane and Sydney.

There have been surprising letdowns elsewhere. At last year's French Open, the sixth-seeded Stosur reached the semifinals and was headed toward victory against Sara Errani of Italy, then seeded 21, but lost in three sets.

Stosur started working with a sports psychologist in 2010 to help her deal with the pressure of playing in Australia and overcoming what she has called "those battles in your own head during matches."

The 28-year-old elaborated on the internal battle at her post-match news conference on Wednesday.

"At 5-2, I felt great," she said. "Then all of a sudden it obviously went away quite quickly."

"Crazy things start popping into your head," she said. "You make an error and you tighten up a little bit, but you try to reset and refocus before that next point."

But that didn't work, and her mind kept churning.

"You probably think a little bit too much," she said. "It's 5-2. You don't want it to go any further than 5-3. You're desperately trying not to make it happen."

Asked if she choked, she sighed.

"At 5-2 up in the third, double break — probably is a bit of a choke, yeah," Stosur said.

After Stosur packed her rackets into her bag and walked off the court, an elated Zheng Jie returned to center court for her victory interview — which turned into an apology.

"Sorry to everyone in the stands," Zheng said to the packed Rod Laver Arena.

Later, the 29-year-old Zheng entered her post-match news conference shaking her head and taking a few deep breaths.

"It's amazing I could come back," she said, and shared what ran through her mind as she was on the cusp of losing.

She told herself: "I need to keep fighting and enjoy the match."

Zheng became the first Chinese player to reach a Grand Slam semifinal at Wimbledon in 2008. She matched that result two years later when she and compatriot Li Na both reached the 2010 Australian Open semifinals.

The No. 6-seeded Li also advanced to the third round Wednesday, beating Olga Govortsova of Belarus, 6-2, 7-5. Li faces Romania's Sorana Cirstea in the next round. Zheng plays 18th-seeded Julia Goerges of Germany.

At 5-foot-4 — Zheng is short compared to some of her opponents. Asked where she honed her fighting spirit, she recited what her coaches told her when she was young.

"I wasn't tall. I wasn't strong. My coaches told me, 'If you want to go far away, you need to keep fighting for every ball — and focus on every point."