Doha, Qatar -- (Sports Network) - The powerful Williams sisters, Serena and Venus, were among Wednesday's round-robin winners at the season-ending $4.55 million Sony Ericsson Championships.

A third-seeded former world No. 1 Serena saw her first action of the week and moved to 1-0 in the four-player Maroon Group with a 6-4, 6-1 pasting of second-seeded French Open and Olympic runner-up Dinara Safina, who is a disappointing 0-2 already this week and has all but been eliminated from semifinal contention this weekend.

In another Maroon Group bout, a seventh-seeded former top-ranked Venus snuck past fifth-seeded Olympic gold medalist Elena Dementieva 6-4, 4-6, 6-3 on Day 2 on the hardcourts at Khalifa Tennis Complex. Venus is now 2-0 and appears well on her way to the semis, while Dementieva fell to 0-1.

On Thursday, a marquee round-robin affair will come when the nine-time major champion Serena battles the seven-time major titlist Venus in a rematch of the Wimbledon final, which was won by Venus. Serena was this year's U.S. Open champ.

Serena is 9-8 all-time against her older sister, including a 2-1 record this year. Oddly enough, the two have never met at the season-ending Championships.

The 27-year-old Serena is the only former Championships titlist (2001) in this year's field. She was also the runner-up in 2002 and 2004.

In some White Group action on Wednesday, eighth-seeded Olympic bronze medalist Vera Zvonareva outlasted fourth-seeded Ana Ivanovic 6-3, 6-7 (5-7), 6-4. A 2-0 Zvonareva is on a path to the semis here, while the 0-2 former No. 1 Ivanovic will, in all likelihood, not make it into the weekend.

An ailing Ivanovic has been battling a virus this week and required some medical attention during the second set on Wednesday.

Ivanovic was this year's French Open champion and Australian Open runner-up and whipped Zvonareva in a final in Linz, Austria just 10 days ago.

In some other round-robin action on Thursday, top-seeded U.S. Open runner-up Jelena Jankovic (1-0) will face sixth-seeded Svetlana Kuznetsova (0-1) and Safina will be opposed by her fellow Russian Dementieva, who topped Safina in the gold medal match in Beijing back in August. Jankovic has already clinched the year-end No. 1 ranking.

Round-robin tennis is the order of the day here through Friday, with the top-two players from each group advancing to Saturday's semifinals and the semifinal victors moving into Sunday's lucrative finale.

The winner of this week's event will collect at least $1.34 million.