ISTANBUL (AP) Victoria Azarenka wrapped up the season-ending No. 1 position in the world by beating Li Na 7-6 (4), 6-3 on Friday in the WTA Championships.
Azarenka secured a spot in the semifinals and will next play Maria Sharapova.
``It's kind of difficult to believe that a little girl from Belarus is on that list,'' said Azarenka, from Belarus. ``It's really incredible achievement. When I started to play tennis I had this big picture in my head that I want to be there. Back then it's so far away. It's like pretty much touching the sky.
``I'm here sitting kind of in the sky, so it's really incredible feeling.''
Agnieszka Radwanska advanced to the semifinals when she edged Sara Errani 6-7 (6), 7-5, 6-4 in a match that lasted nearly 3 1/2 hours. The fourth-ranked Radwanska will play Serena Williams on Saturday.
Sharapova swept past Sam Stosur 6-0, 6-3 on the final day of round-robin play but Azarenka's win means that the Russian will not be able to wrest the No. 1 ranking form her.
Azarenka won the Australian Open in January and had been ranked No. 1 for most of the year, except for a brief period after Sharapova won the French Open.
Sharapova had already qualified for the semifinals of the elite, eight-woman event and has won all three of her round-robin matches.
The Russian rolled through the first set, allowing Stosur only five points. Stosur was an alternate who replaced defending champion Petra Kvitova, who withdrew because of illness.
``I certainly didn't want to play as long a match as I did in the previous round. I wanted to do a better job of a few things and I think I did,'' said the second-ranked Russian.
Stosur put up more of a fight in the second set, but Sharapova ended it with a smash.
Errani finished the tournament with one win and two defeats. The seventh-seeded Italian won a game in the middle set that went to nearly 15 minutes but was not able to use that momentum and dropped her serve to fall behind 6-5.
Radwanska served out the set and opened up a decisive 3-0 lead in the final set to secure a place in the semifinals.
``I had to play my best tennis until the end of the match because every game was a big fight,'' Radwanska said.
Williams was undefeated in three matches in her Red Group and didn't play on Friday.
The match between Radwanska and Errani lasted 3 hours, 29 minutes and was the longest recorded best-of-three-set match in WTA Championships history.
The previous record was 3:24, set in the 2007 final when Justine Henin beat Sharapova 5-7, 7-5, 6-3. The event, however, also used a best-of-five format for a while and had longer matches.
``Altogether I am exhausted,'' said Radwanska, who had another three-hour-plus match in the previous round. ``I really need to be ready for tomorrow.''