Top seed Serena Williams celebrated her 23rd birthday with a gritty 4-6, 7-5, 6-4 win over Russian Svetlana Kuznetsova in the China Open final on Sunday.

The former world number one fought off a championship point before recovering to claim the title as she fired down 18 aces but struggled for consistency throughout the match.

"I was psycho out there. I was trying to hit every ball as hard as I could and I couldn't get a first serve in," said the six-time grand slam champion.

"I think the key to victory today was I never gave up. I really didn't want to lose today," said Williams, wearing a bright orange T-shirt saying: "The ball was in".

The reference was to her U.S. Open quarter-final defeat to Jennifer Capriati during which umpire Mariana Alves called "advantage Capriati" after Williams hit a backhand winner.

A questionable call cost Williams the first set on Sunday and she showed her frustration by smashing her racket into her chair but this time she battled back to clinch victory.

UNFORCED ERRORS

Williams was taken to the brink of defeat, though, as she struggled to stem a flow of unforced errors in the second set leaving U.S. Open champion Kuznetsova with a championship point but the Russian missed her chance.

"I just said, 'Fight and hold serve here,' and that is what I had to do," said Williams, who broke to go 6-5 up and served out to love to take the set.

"I had many chances in the second set and sometimes she served well and there's nothing you can do," Kuznetsova said.

The second-seeded Russian looked deflated early in the third set as Williams faced into a 4-0 lead and although Kuznetsova fought back to 5-4 Williams took the title with two big serves.

"She was also tired and I saw it, said 19-year-old Kuznetsova. "The thing is I lost focus, maybe.

"I lost because I missed some balls I should not have missed... but I think I made her move, I made her work for it."

It was the first defeat in 15 matches for Kuznetsova, who had to contend with her fair share of questionable calls and a raucous crowd that generally favoured Williams.

The capacity crowd sang 'Happy Birthday' and cheered wildly, drowning out line calls, but the modest Russian said: "Today, I felt this crowd was nice, they were supporting who was down".

Williams noted that many aspects of her game need work but said she was happy to taste victory after a long drought.

"I'm excited because I haven't won a title since March and that's not like me."