Serena reaches WTA Championships semis

Istanbul, Turkey ( - Mighty Serena Williams went a perfect 3-0 in round-robin play this week and will compete in the semifinals this weekend at the season-ending $6.5 million WTA Championships.

Thursday's nightcap in Istanbul saw the world No. 1 and reigning Championships champion Williams flatten fifth-seeded 2011 titlist Petra Kvitova of the Czech Republic 6-2, 6-3.

The high-flying Williams is now a brilliant 76-4 this year.

The three-time Championships titlist and two-time runner-up beat Maria Sharapova in last year's finale in Istanbul.

Also on Day 3, eighth-seeded German Angelique Kerber (1-1) whipped third- seeded Pole Agnieszka Radwanska 6-2, 6-2 and fourth-seeded Chinese Li Na (2-0) held off resurgent seventh-seeded Serb Jelena Jankovic 6-3, 2-6, 6-3 in Thursday's opener. The former U.S. Open runner-up Jankovic dropped to 1-1 for the week.

Last year's Wimbledon runner-up Radwanska went winless in her three round- robin matches at the spacious Sinan Erdem Dome.

This week's four-woman Red Group was led by the U.S. and French Open champion Williams and also includes Radwanska, Kvitova (1-1) and Kerber. Friday's Kvitova-Kerber winner will join Williams in the semis coming out of the Red Group.

Second-seeded Australian Open champion Victoria Azarenka (1-1), who was the 2011 Championships runner-up to Kvitova, spearheads this week's four-player White Group, which also features the Aussie Open runner-up Li, sixth- seeded former French Open finalist Sara Errani (0-2), and Jankovic. The two semifinal spots out of the White Group will be up for grabs on Friday.

Some other Friday action will pit Azarenka against Li and Errani versus Jankovic.

Istanbul is hosting this elite eight-woman event for a third and final time before it shifts to Singapore next year.

Round-robin play will be staged through Friday, followed by semifinal action on Saturday, and a lucrative final on Sunday.