Nikolay Davydenko reached the Qatar Open quarterfinals by beating fourth-seeded Mikhail Youzhny 7-5, 6-3 on Wednesday.
Once ranked as high as No. 3, Davydenko has struggled in recent years because of injuries. But the Russian combined a consistent first serve with aggressive play to unnerve the 25th-ranked Youzhny.
Gael Monfils defeated third-seeded Philipp Kohlschreiber of Germany 6-4, 2-6, 6-4.
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.
"Tough match," said Davydenko, who won the tournament in Doha three years ago. "Maybe we didn't start well with so many mistakes. I know against Russians when you play in second round, it's not easy."
The 44th-ranked Davydenko said he was targeting a place in the top 20 this year after failing to win a tournament in 2012.
"If I really concentrate and (practice) and play, I want to see results," he said.
Monfils, who has fallen to 77th in the rankings after knee troubles forced him to cut short his 2012 season, used his powerful serve to take the lead. But in the second set, the Frenchman appeared to get frazzled by a new rule that requires players to serve in 25 seconds.
Monfils repeatedly argued with the umpire after a warning that he was taking too long, and Kohlschreiber soon took a 5-1 lead in the set.
In the third set, Monfils had four of his 10 aces and Kohlschreiber started making more unforced errors. The German also missed three early chances to break Monfils.
"I was very pleased with my game," said Monfils, who beat Rafael Nadal last year to reach the Qatar Open final. "I didn't know what to expect. I am 100 percent."
Nadal is sidelined because of a virus, and he's not expected to play until February.