Top-ranked Caroline Wozniacki advanced to the third round of the Madrid Open by beating Bojana Jovanovski of Serbia 6-4, 6-4 Tuesday.
Wozniacki broke her opponent twice in the first set and three times in the second, while saving eight of the 11 break points she faced.
"Jovanovski is very young and I hadn't played her before," Wozniacki said. "She made some unforced errors, although later in the match she got better and didn't make it easy for me."
Samantha Stosur of Australia also advanced, beating Daniela Hantuchova of Slovakia 7-6 (1), 7-5. Stosur also beat Hantuchova in Stuttgart last month.
"I've played some of my best matches of the year on red clay so I'm happy," Stosur said.
On the men's side, Juan Martin del Potro of Argentina overcame a hip problem to beat 13th-seeded Mikhail Youzhny of Russia 6-1, 3-6, 6-3 to reach the second round, while Jo-Wilfried Tsonga of France defeated Pere Riba of Spain 6-4, 6-2 to make the third round.
Del Potro, the 2009 U.S. Open champion who missed much of last season after having wrist surgery, appeared to struggle in the second set and called a physiotherapist for on-court treatment.
"I have some pain in my hips and I've been trying to play through it, trying to win despite the pain," Del Potro said.
The Argentine player said he has been struggling with the problem since winning Sunday's Estoril Open final against Fernando Verdasco.