Doha, Qatar - Serena Williams secured a perfect group record at the Sony Ericsson Championships Thursday after claiming a 6-2, 6-4 defeat of Elena Dementieva. Williams, who secured the year-end world number one title a day earlier when rival Dinara Safina was forced out of the year-end event with back pain, added her Maroon group victory to those she scored earlier over Svetlana Kuznetsova and her sister Venus.
US Open finalist Caroline Wozniacki came through a gruelling, physical struggle against substitute Vera Zvonareva which was marked by fitness issues.
The Danish winner produced a fighting 6-0 6-7 6-4 against the Russian, who substituted her compatriot Safina.
Final standings for the weekend semi-finals will be determined after Friday's last group matches, with both Wozniacki and Williams in secure positions.
World number four Wozniacki suffered with cramping as she played her sixth hour so far this week. Zvonareva was treated for a second-set nosebleed in the two-hour, 48-minute struggle in the Gulf.
Wozniacki nearly lost her form when the cramps sent her to the floor late in the match. But the teenager soldiered on to earn a third match point and ultimately claim the tightly-wound contest.
