Serena Williams is "a favorite" to win the WTA tour championships in Istanbul next week, former world No. 1 Caroline Wozniacki said after winning the Kremlin Cup in Moscow on Sunday.

Wozniacki finished runner-up to Kim Clijsters at the tour championships in Doha in 2010, her second of three appearances at the event, but the Dane's tumble to 11th in the rankings this season means she will miss out.

"Serena is definitely a favorite always, indoors she's serving well and she has good shots," Wozniacki said, adding that it was "tough to say" who would come out on top in Turkey.

Wozniacki said she was disappointed not to have a place in Istanbul but was aiming to play well in the second-tier tournament of champions in Sofia, which starts October 30.

"Obviously you want to be playing in Istanbul, no doubt that's the goal at the beginning of the season," she said.

"But that didn't happen this year and that's just something that is sports sometimes. I'm going to go to Sofia and just do my best."

Wozniacki's defeated opponent in the Moscow final was Australian world No. 9 Sam Stosur, who will be in Istanbul as first alternate for the tournament, to step in if one of the top eight automatic qualifiers retires.

"As far as Istanbul goes, I'm going there tonight, so I have one day to prepare and then if I have to play, then I'll be as ready as what I can be," Stosur said.

"Time will tell whether or not I get to play another match this year."

Wozniacki beat Stosur 2-6, 6-4, 7-5 to win the $740,000 Premier tournament on Moscow's indoor hard courts.