Tokyo, 25 September 2011 | AFP

US Open champion Samantha Stosur said her win in New York offered no guarantees of success as she gears up to face a high-quality field in Japan’s Pan Pacific Open starting on Sunday.

The 27-year-old beat Serena Williams earlier this month to become the first Australian woman to win a grand slam title since 1980.

But Stosur, ranked number seven in the world, faces a stiff challenge in Japan with seven of the world’s top 10 players – including the top four – in the draw for the $2.05 million tournament in Tokyo.

“This week is a new week. You win a week before and there are no guarantees for the next week,” Stosur said.

“So I have to get back on the practice court and keep training hard and being fully prepared for the first round,” she said.

Denmark’s world No.1 Caroline Wozniacki, who lost to Williams in the US Open semi-finals, will be aiming to defend the title she won last year, which helped her reach the top ranking.

Crowd favourite Maria Sharapova, who won the title two years ago and was also champion in 2005, returns as the No.2 seed after a fine season where she’s reached her highest ranking since returning from shoulder surgery in 2009.

The Russian will be keen to banish memories of her disappointing first-round defeat to veteran home favourite and 1995 champion Kimiko Date-Krumm last year.

The tournament also features world numbers three and four, Victoria Azarenka of Belarus and Russia’s Vera Zvonareva, as well as Wimbledon champion Petra Kvitova of the Czech Republic.

It comes just over six months after Japan was hit by an earthquake and tsunami that devastated large areas of the northeast, leaving almost 20,000 dead or missing and sparking the worst nuclear crisis since Chernobyl.

A number of sporting events were cancelled after the triple calamity but Zvonareva said the players were happy to play in Japan.

“I think this year is special for everybody. I think everyone had doubts about the tournament happening when the terrible disaster happened,” she said.

“I think we are all happy that we have been able to come here and play here and actually have this event. Of course, as usual, I will try my best like I always do.”