LOS ANGELES (AP) -- Kim Clijsters couldn't believe what she'd just done. Clijsters stunned top-seeded Serena Williams 7-5, 6-3 to win the season-ending WTA Championships on Monday night, handing Williams only her fifth loss of the year.
Williams' 18-match winning streak was snapped largely because of 44 unforced errors, especially on the backhand side. She finished with a 56-5 record, French, Wimbledon and U.S. Open titles and ended the year as the world's top-ranked player.
Clijsters, a 19-year-old Belgian who rose to No. 4 in the rankings, only managed six winners to 19 by Williams, but she converted five of 10 break chances in the nearly 1 1/2-hour match at Staples Center.
''It's been an incredible week for me,'' said Clijsters.
, who defeated No. 2 Venus Williams in the semifinals when she retired with an injured leg. Clijsters had never beaten Serena Williams in five previous meetings.
''This is definitely my biggest win and it feels incredible. I had goosebumps all over my body,'' Clijsters said.
Clijsters became the first player since Martina Hingis in the 2001 Australian Open to beat the Williams sisters in the same tournament and only the fourth ever. She also tied the record for fewest games (14) lost en route to the title.
''It's still pretty amazing for me to realize I won this,'' she said.
Clijsters didn't drop a set in four matches and earned $765,000 from the $3 million purse.
''She's always had a lot of talent,'' Williams said. ''She has a very good future. We'll see what next year will bring.''
After a tired Williams barely got a forehand back, Clijsters rushed the net and put away a forehand winner on match point. She dropped her racket and buried her face in her hands in disbelief. Clijsters then fired a ball into the crowd and gave a thumbs-up sign.
There were seven service breaks in the first set, when Williams led 5-3 before losing the final four games.
In the second, Clijsters served at 2-2. At deuce, she daringly tried a drop shot that landed on the line, then Williams returned Clijsters' serve long and Clijsters led 3-2. Williams dropped her serve at love to trail 4-2.
Clijsters survived a break point at 30-40 on her serve to force deuce. She hit a service winner, then Williams netted a backhand service return to trail 5-2. Williams held in the next game for 5-3 before Clijsters served out the match.
''I tried to make her make the mistakes,'' Clijsters said. ''She wasn't moving as well as she normally does.''
Clijsters joined Americans Chanda Rubin and Meghann Shaughnessy, Patty Schnyder of Switzerland and Belgian Justine Henin as the only players to beat Williams this year.
The Belgian teenager has played particularly well in the last month, winning titles in Filderstadt, Germany, and Luxembourg leading up to Los Angeles. She won her first title of the year in Hamburg, beating Venus Williams in a three-set final.
This week, Clijsters' boyfriend, men's No. 1 Lleyton Hewitt, will try to duplicate her feat in the season-ending Masters Tennis Cup in China. Because of the time difference, Clijsters wasn't able to call him and share her big news.
Serena Williams won the tournament a year ago in Germany when Lindsay Davenport defaulted because of injury. Williams was coming off a tough three-set semifinal win over No. 3 Jennifer Capriati on Sunday.
''I was happy to make it this far. This whole week I don't think I played very well at all,'' Williams said. ''I feel like I'm 98 years old. Everything is broke and I'm ready to go home. An old lady in a young woman's body.''
Williams earned $382,000 as runner-up, pushing her season earnings to a record $3,657,826. That bettered the $3,457,049 earned in 2000 by Hingis. A victory would have made Williams the first woman to earn more than $4 million in a year.
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