By John O'Brien

SINGAPORE (Reuters) - Agnieszka Radwanska was left to rue a failure to take her chances when she stumbled to a 7-5 1-6 7-5 defeat against Russia's Svetlana Kuznetsova in the opening match of her WTA Finals defense on Monday.

The Polish world number three led 4-1 in the first set and held a match point in the 10th game of the decider but was unable to capitalize both times as her opponent dug deep to claim victory in an absorbing contest.

"Well, of course it's very disappointing, especially that I had chances and just let them slip away," the 27-year-old told reporters.

"To turn up like this, against players like Sveta (Kuznetsova), if you don't take your chances, you're not going to be a winner."

Radwanska, however, knows all is far from lost after defeat in her White Group opener. Last year, the Pole advanced to the semi-finals with a 1-2 record and still went on to claim the biggest win of her career, beating Petra Kvitova in the final.

"I still have a chance, especially as I was two losses down last year," she added.

"But, of course, at the moment you're always thinking about the match that you just lost, so I think I need to cool down first and then I will think about what I have to do to go to the semi-finals."

Despite the defeat, Radwanska was satisfied with her overall performance in the Singapore Indoor Stadium and believed the result could have been different had a couple of key moments gone her way.

"Overall, it was a good, tough match. I think a lot of things were happening," she added.

"I could play a little bit better. Couple of mistakes in the bad moments and not the right decisions I guess, and, yeah, that cost me a lot."

French Open champion Garbine Muguruza and first-time finalist Karolina Pliskova are the other two players in Radwanska's pool at the elite eight-woman event.

(Editing by Ian Chadband)