DOHA, Qatar — After struggling with injuries last year, Nikolay Davydenko and Gael Monfils are playing some of their best tennis at the Qatar Open.
Davydenko reached the quarterfinals by beating fourth-seeded Mikhail Youzhny 7-5, 6-3. He was joined by Monfils, who upset third-seed Philipp Kohlschreiber 6-4, 2-6, 6-4.
Second-seeded Richard Gasquet rallied past 55th-ranked Grega Zemlja of Slovenia 6-7 (7), 6-4, 7-6 in a match that lasted nearly 3 hours.
Davydenko, once ranked as high as No. 3, combined a consistent first serve with aggressive play to unnerve the 25th-ranked Youzhny.
Davydenko broke his opponent to take a 6-5 lead in the first set and won when Youzhny hit a forehand into the net. Davydenko kept the momentum going into the second set, forcing Youzhny to save a break point in the first and third games. At 2-2, Davydenko won three straight games to take control.
At Shenzhen, China, top-seeded Li Na advanced to the Shenzhen Open quarterfinals with a 6-3, 6-4 win over Julia Cohen of the United States in the second round.
The Chinese star overcame five double faults and struggled with her serve during the 94-minute match.
Li will play eighth-seeded Bojana Jovanovski of Serbia.
No. 2-seeded Marion Bartoli also advanced by defeating Swiss qualifier Stefanie Voegele 7-5, 6-4. Bartoli will take on fifth-seeded Klara Zakopalova of the Czech Republic for a place in the semifinals.
At Brisbane, Australia, top-ranked Victoria Azarenka opened her 2013 season with a 6-3, 6-3 win over Sabine Lisicki to join No. 3 Serena Williams and fourth-seeded Angelique Kerber in the Brisbane International quarterfinals.
American Sloane Stephens had a 6-3, 6-4 win over Sweden's Sofia Arvidsson to set up a quarterfinal against Williams.
Azarenka won her first major at the Australian Open last year during a 26-match winning streak to start the season and spent most of 2012 atop the women's rankings.
Azarenka will play Kazakh qualifier Ksenia Pervak, who has ousted former No. 1 Caroline Wozniacki and Urszula Radwanska in matches decided by third-set tiebreakers.
At Perth, Australia, Bernard Tomic upset top-ranked Novak Djokovic 6-4, 6-4 but Australia lost to Serbia 2-1 at the Hopman Cup.
Ana Ivanovic evened the round-robin event by overwhelming Australian 16-year-old Ashleigh Barty 6-2, 6-3. Barty made a positive start, but once Ivanovic made the first break to lead 4-2 she took control. The Serbians combined to win the mixed doubles 6-4, 6-7 (8), 10-6.
Today, the United States team of John Isner and Venus Williams will play the Spanish pair of Fernando Verdasco and Anabel Medina Garrigues for a place in Saturday's final. Australia will face Italy.