in the first of two semifinals 5-7, 6-3, 6-4. Afterwards the second ranked Serena Williams ousted the fourth seeded Caroline
Wozniacki of Denmark in the second semifinal 6-4, 0-1 when Wozniacki retired in the second set with a stomach strain.
Wednesday in the round robin competition, Serena Williams defeated Venus Williams 5-7, 6-4, 7-6(7-4). Venus Williams led 6-5 in the final set before Serena Williams raised the level of her game in the end to take the match which lasted nearly three hours.
And while Serena Williams has this year won both the Australian Open and Wimbledon and is set to return to the WTA Tour's top ranking next week, her sister Venus Williams has fallen to seven in the WTA Tour rankings and gone without a singles grand slam win this year while battling an on-again off -again knee injury.
Venus Williams won her lone two WTA Tour singles titles of this year in February at Dubai and Acapulco before turning in several suspect results due to a possible knee problem including a May 6-0, 6-4 third round French Open exit.
The 29 year old Venus Williams required treatment on her knee during her semifinal match Saturday and could be at a major disadvantage to her 28 year old sister Serena Williams as only one of four of the younger sister's singles matches this week have gone to three sets while all four of Venus Williams' singles matches went three sets.
If Venus Williams can recover from fatigue and her knee injury, she could have a good chance against Serena Williams, but only if she serves well and turns in a low error count. The older sister failed to do either when she fell to her younger sibling in the summer in the Wimbledon final 7-6(7-3), 6-2.
Head to head Serena Williams leads Venus Williams 12-10. A win today for Venus Williams would be certainly impressive. However the American would be only the third player this decade to win back to back WTA Tour year end tournament singles titles.
The Belgians Kim Clijsters and Justine Henin took the year end singles titles in 2002-2003 and 2007-2008 respectively.