Williams beat eighth-seeded Nicole Vaidisova of the Czech Republic 6-4, 7-6 (7), and the top-seeded Kuznetsova defeated Vera Dushevina 6-2, 6-2.

Last Friday, Kuznetsova beat Williams in the quarterfinals of the Porsche GP in Stuttgart, Germany.

Elena Dementieva of Russia reached the semifinals at the Kremlin Cup for the fifth straight time, beating Belarusian teenager Victoria Azarenka 7-6 (4), 6-2. She will next play Dinara Safina, who eliminated Vera Zvonareva 6-2, 3-6, 6-3.

On the men's side, Janko Tipsarevic of Serbia beat Radek Stepanek of the Czech Republic 6-4, 3-6, 6-3 to reach the semifinals, and fourth-seeded Paul-Henri Mathieu eliminated Florent Serra of France 6-3, 6-3.

Eighth-seeded Philipp Kohlschreiber retired with a back injury after losing the first set 6-3 against Michael Berrer.

Williams pressured Vaidisova from the start and didn't allow the Czech to hold her serve without being taken to deuce or facing a break point until the fifth game of the second set.

In the eighth game, Williams was broken and trailed 5-3, but she broke back and saved a set point on a deuce in the 12th game to force a tiebreaker.

Vaidisova saved three match points in the tiebreaker before netting a forehand to lose the match.

Kuznetsova, the 2004 U.S. Open champion, won five consecutive games in each set and sealed the victory with an overhead smash.

"Tomorrow it will be a tough match," Kuznetsova said of her first Kremlin Cup semifinal match. "Williams is improving her form and is tough at the end of the season."

Dementieva, the runner-up in 2001 and 2004, won four consecutive games in the second set. She had five aces.

The 18-year-old Azarenka, who upset second-seeded Maria Sharapova in the second round, never threatened Dementieva.

Safina, the sister of Marat Safin, easily won the first set and was level at 3-3 in the second before losing three straight games. The 17th-ranked Russian broke twice in the third set to advance to her second semifinal match in her hometown. She lost to eventual champion Mary Pierce in 2005.