World number one Serena Williams marched into the semi-finals of the WTA Championships on Thursday with a comfortable win over Elena Dementieva while sister Venus kept her title hopes alive long after midnight.

Serena's 6-2 6-4 victory completed a 100 percent record for the American in Maroon Group and confirmed her as the first player through to the last four at the season-ending showpiece.

Venus, who suffered narrow defeats to Dementieva and Serena in her first two matches, beat Svetlana Kuznetsova 6-2 6-7 6-4 in a hard-hitting clash and must now sweat on Friday's results before knowing whether she will be in action at the weekend.

Feisty teenager Caroline Wozniacki remained undefeated on her debut at the $4.5 million Championships after beating Russian stand-in Vera Zvonareva in a White Group match that at times resembled a hospital casualty department.

The 19-year-old Dane eventually won 6-0 6-7 6-4 but played the last four points virtually on one leg. She was in tears after suffering agonising cramps in her heavily-bandaged left thigh and could barely hobble to the net to shake hands.

Zvonareva, a replacement for fellow Russian Dinara Safina who withdrew with a back injury, was also in the wars, needing treatment in the second set as blood oozed from her nose.

The Russian later withdrew with an ankle injury meaning second reserve Agnieszka Radwanska of Poland will get a run out against semi-final hopeful Azarenka on Friday.

"I have absolutely no idea how I pulled it through, but I'm very happy about it," said surprise U.S. Open runner-up Wozniacki, who may still need to beat Serbia's Jelena Jankovic on Friday to clinch a semi-final spot."

"I'm gonna do everything I can to get ready for tomorrow," added the world number four. "I'm just going to do everything that physio and the doctors are saying, drinking a lot of fluids, eat some good food, stretch, get some massage, get some ice massage, take a salt bath, everything."

There were no such dramas for Serena who recovered from an early service break to win seven games in a row against Dementieva, a player she had lost to three times this year.

ATLANTA – The Georgia Tech Women’s Tennis will host a rare fall dual match against the U.S. Junior Nation Team Saturday, Oct. 31 at the Bill Moore Tennis Center beginning at 12:00 p.m.

Unlike the usual fall tournament format, Wednesday’s match will be played in dual-match fashion beginning with two sets of doubles matches followed by singles pairings.

“It is a great opportunity to have the U.S. Junior National Team on our campus to get a look at Georgia Tech and see all the great things they have to offer,” head coach Bryan Shelton said. “It will also be a great experience for our girls to play against some of the nation’s best.”

The Junior National Team is sending eight of the top junior players from across the nation to compete against the Yellow Jackets All eight players are Blue Chip recruits who rank in the top 10 nationally in their respective graduating classes. The team is composed of five sophomores, including four of the top five sophomores in the nation, and three juniors.

The sophomores are led by Lauren Davis, who is the top-rated sophomore in the nation. The Gates Mills, Ohio native holds an impressive 78-5 record in junior play. Grace Min, currently the second-best sophomore in the country, has compiled a 32-15 overall record, hails from Lawrenceville, Ga. Chanelle Van Nguyen is ranked No. 3 in the sophomore class. She is from Miami, Fla. and has an overall junior record of 24-13. Kyle McPhillips, hailing from Willoughby, Ohio, comes in as the No. 4 rated sophomore, and is second in the Great Lakes Region behind only Davis. Breaunna Addison, a native of Boca Raton, Fla., is ranked No. 8 in the sophomore class and holds a 41-12 overall record.

The juniors are led by Lake Forest, Ill. native Monica Turewicz. She is currently No. 2 in the junior class with a total record of 38-14. Lauren Herring, who hails from Greenville, N.C., comes in as the No. 5 junior in the nation. She is the top-rated junior in the Southeast Region and holds a 26-16 record. Emina Bektas is the seventh-rated junior in the U.S. She is from Indianapolis and is the top player from the state of Indiana. Bektas has compiled a junior record of 49-16.

Fans are encouraged to not only come out and support the Jackets, but also to get a look at some of the best junior tennis players in the country. Admission to all Georgia Tech tennis matches is free.