ROME (AP) -- Rafael Nadal hardly had to get his socks dirty to extend his winning streak to 16 matches.
Back to being the best player on tour over the last month, Nadal advanced from his opening match at the Italian Open on Wednesday when Nicolas Almagro retired in the first set with an apparent injury.
Nadal was leading 3-0, 15-30 when Almagro bent over toward the red clay court and grasped his left knee.
Nadal went over to Almagro's side of the net to ask what was wrong and consoled his opponent. Almagro then got some medical attention at his chair but quickly retired from the second-round match.
The fourth-ranked Spaniard remained on court for a practice session.
Nadal has won consecutive clay-court tournaments in Monte Carlo, Barcelona and Madrid. He's aiming for an eighth title at the Foro Italico as he prepares for the French Open, which starts in less than two weeks.
Nadal will next face either 13th-seeded Jack Sock or Jiri Vesely of the Czech Republic.
The 73rd-ranked Almagro had come through qualifying.
Also, seventh-seeded Kei Nishikori beat David Ferrer 7-5, 6-2.
Nishikori showed no lingering pain from the right wrist injury that prompted him to withdraw from the quarterfinals in Madrid last week.
"My wrist is OK now. I assume to be 100 percent now," Nishikori said.
In women's action, second-seeded Karolina Pliskova defeated Lauren Davis of the United States 6-1, 6-1, and sixth-seeded Simona Halep beat Laura Siegemund of Germany 6-4, 6-4.
Also, eighth-seeded Elina Svitolina eliminated Alize Cornet of France 6-4, 7-6 (11), and 15th-seeded Kiki Bertens beat American qualifier CiCi Bellis 6-4, 6-0.
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