France's Mary Pierce took down compatriot Amelie Mauresmo 2-6, 6-4, 6-2 in their last group match on Friday to complete the semi-final line-up at the WTA Championships.
With the victory, Pierce won the round-robin Green Group and now plays top-ranked Lindsay Davenport, who finished second in the Black Group behind defending champion Maria Sharapova.
Mauresmo will face Sharapova, who won her group by defeating Davenport on Thursday.
But on Friday, an exhausted Sharapova showed none of her stellar form, going down quickly to Nadia Petrova 6-1, 6-2.
Sharapova said the winner of the event would be the player who can gut it out after a long season.
"This is the kind of tournament where all the soldiers are down and it's whoever can get up [will win]," she said. "I can't sleep. Throughout the whole day I'm like a walking zombie."
The 30-year-old Pierce finished her group with a 3-0 record, after earlier victories over Kim Clijsters and Elena Dementieva.
Although both Pierce and Mauresmo had already qualified for the semi-finals, they contested a hard-fought match, with Mauresmo mixing serve-and-volley tactics and Pierce hammering her countrywoman from inside the baseline.
Mauresmo had Pierce back on her heels during the first set, but in the final two sets Pierce served extremely well, passed with efficiency and took apart Mauresmo's backhand.
Pierce broke twice in the third set. She broke to 3-1 when Mauresmo misses a backhand volley and then again to win the contest on her third match point when Mauresmo missed a forehand.
"These kind of matches are tough to play," said Mauresmo. "I still had the opportunity to win but after I lost the second set, it was tough to keep up the intensity in the third set.
"Since we were both in, you don't want to push yourself too much," she added.
It was only the second time that France has had two WTA Championships semifinalists, the other time being in 1997.
Pierce, making her first Championships appearance since 1999, has had a great year, reaching the French Open and U.S. Open finals and winning two titles.
She is the only player to have won all three matches in her group here but has a 3-8 lifetime record against Davenport entering the contest.
However, Pierce did beat Davenport the last time they played at the French Open.
"I'm really excited about that, really proud, feeling good after winning all my matches in this group," said Pierce, "It's definitely going to be a fun match against Lindsay. She's got a great serve and real heavy groundstrokes."
Sharapova and Mauresmo have played only once before, the Frenchwoman winning here last year in straight sets in a match with no significance because the semi-finals had already been decided.
"She's a complete player," Sharapova said. "There's no big weakness in her game. I have to be ready for a tough match."
World number two Kim Clijsters took down Russia's Dementieva 6-2, 6-3 but did not qualify for the semi-finals.
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