Venus Williams will play Vera Zvonareva in the final of the WTA Championships after both women achieved difficult three-set victories on Saturday.
Wimbledon champion Williams overcame Serbian world number one Jelena Jankovic 6-2, 2-6, 6-3, and Zvonareva beat fellow-Russian Elena Dementieva 7-6, 3-6, 6-3.
The match between Williams and Jankovic produced high-quality rallies as both players defended well but attacked at every opportunity.
Jankovic made a slow start and produced numerous errors, while her American opponent's strong forehand helped her to break twice to lead 4-1.
Jankovic raised her game and, although it was too late to save the first set, she took the second.
She recovered from 0-40 in the first game, winning nine of the next 10 points and going on to lead 3-0. She held off another threat after Williams broke for 3-2, saving two game points for 3-3 before breaking Williams again for 4-2.
The final set was the most closely contested, with Williams breaking for 2-1 and then fighting off five break points to hold for 4-2. As errors once more began to appear in Jankovic's game, Williams broke a final time for the match.
"What got me through the match was being consistent at the right time," Williams told reporters. "My game is about being aggressive and taking chances but today I really needed to put a lot more balls in play and be a little smarter."
Jankovic admitted that being unable to convert her break point chances in the third set was crucial.
"It was very frustrating for me because I had so many opportunities, so many breakpoints," she said. "Really a lot of chances but I didn't do anything. I didn't convert any in my favour which was the key of the match in that third set, especially."
In the other semi-final neither player hit a single ace in the two-hour-20-minute battle as they both struggled to produce their best tennis.
The first set was particularly disappointing, with breaks in eight of the 12 games and seven of the last nine points in the tiebreak going against serve.
Fifth seed Dementieva served for the first set twice, at 5-4 and 6-5, and she held a set point in the tiebreak at 7-6 before losing it 9-7.
Both players settled down and produced some decent rallies, although not on a consistent basis. Zvonareva dropped her serve with a double fault to fall behind 2-0, then wasted a break point when down 3-1.
The eighth seed quickly regained the upper hand in the final set, breaking for 2-0 when Dementieva made a backhand error.
Although Dementieva broke back at 4-2, when a blistering return forced an error, another backhand error allowed Zvonareva to break once more and serve out the match to love.
"The match was very, very tough," said Zvonareva. "I think you have to try to keep your concentration throughout the whole match. Yeah, I had some games not so good, but overall I was able to manage myself and my game pretty good."