Sam Stosur is disappointed with her lack of titles this season after being unable to follow up her maiden Grand Slam success last year, she said Monday.

Stosur achieved a career-high ranking of world No. 4 last season and won the U.S. Open, beating local favorite Serena Williams 6-2, 6-3 in the final, but has not won a title since and slipped to ninth in the rankings.

"This year does feel a little more disappointing than last year because of the results," Stosur said ahead of the Kremlin Cup in Moscow, her last confirmed tournament of the season.

"It hasn't been that bad. I just haven't had the really big result or the big win like the U.S. Open, so without that everything else seems that little bit lower than previous years."

Stosur arrived in Moscow off the back of a surprise semifinal defeat in Osaka, where she was top seed but lost to world No. 134 Chang Kai-Chen, which she described as "very disappointing."

"You're kind of expected to win that one. Having said that, my opponent played extremely well and I didn't have my best day," she said.

The eventual winner was Heather Watson, who became the first British woman to win a WTA singles title for 24 years.

"Obviously that's huge for her and obviously for her country. In Britain, they want to have more top-ranked players and players winning tournaments, so it's nice they've been able to achieve that on the women's side," Stosur said.

The Australian is seeded top in Moscow, where she has a first-round bye and will play either France's Alize Cornet or an as-yet unknown qualifier in the second round.

Stosur must defend her ninth spot in the rankings from 10th-ranked Marion Bartoli, also in the Kremlin Cup, as the ninth-placed player will be first substitute for the tour finals in Istanbul.