U.S. Open champion Kim Clijsters beat top seed Caroline Wozniacki of Denmark 6-3, 5-7, 6-3 to win the WTA Championships final on Sunday.

The Belgian, 27, who won the tournament for a third time, maintained her perfect record in finals since coming out of retirement midway through 2009 with her sixth title.

"It was a tough match," said Clijsters. "It is disappointing for Caroline but she has a great future ahead. I'm glad I won and it must be disappointing for Caroline, but I don't know how many more years I'm going to keep doing this."

For Wozniacki, the result gave more ammunition to critics who believe the 20-year-old's position as No. 1 is a false one.

"I've had a fantastic year," Wozniacki said on Sunday. "I won six tournaments. I've beaten so many good players. You know, you cannot win every match. I've made the finals of the Championships, and I lost one match today. You know, I cannot do anything about it now. I will come back in the off season and train, but right now I'm proud of my season."