Iga Swiatek continued to make it look easy at the Madrid Open, reaching the round of 16 with a comfortable 6-3, 6-2 win over Bernarda Pera on Sunday. (More Tennis News)

The world No. 1 conceded only one break point and converted on four of the 13 that she earned against the 32nd-ranked American at the “Magic Box” center court.

Swiatek had beaten Julia Grabher by the same score in her opening match in Madrid. The Polish player has won six straight matches in her clay-court season while dropping only one set.

“I wouldn't say it was easy,” Swiatek said. “Every match is tricky here. I'm happy that I'm getting my rhythm. Playing against a lefty is never easy ... but I'm pretty happy that I was disciplined and focused.”

Swiatek will next play either 22nd-seeded Zheng Qinwen or 16th-seeded Ekaterina Alexandrova.

Third-seeded Jessica Pegula had to work harder on her way to a 6-4, 7-6 (2) win over Marie Bouzkova. The American saved 12 of the 14 break opportunities that she conceded against her 31st-ranked opponent.

“It was definitely a long, physical game,” Pegula said. “It's always hard to play Marie. We always have tough, long matches. I knew it was going to be very difficult.”

In the men's draw, two-time Madrid Open champion Alexander Zverev cruised past qualifier Hugo Grenier 6-1, 6-0 in less than an hour. Zverev lost last year's final to Carlos Alcaraz, who could be his next opponent in the Spanish capital. Alcaraz faces 26th-seeded Grigor Dimitrov later Sunday.

“Today I felt great,” Zverev said. “Maybe Hugo was a bit nervous, first time in the third round at a Masters and that is big for any player. In general, I am happy that I kept my composure and that I am through.”

Zverev, who had 26 winners and broke Grenier's serve six times, won his Madrid titles in 2018 and '21. He is 21-3 in the tournament, having reached the quarterfinals in all five of his previous appearances.

Fifth-seeded Andrey Rublev improved to 10-1 on clay this season with a 6-2, 7-5 win over Yoshihito Nishioka. Rublev, who reached the quarterfinals in Madrid last year, won the Monte Carlo Masters two weeks ago.

He will next face Karen Khachanov, the 10th-seeded player who defeated home-crowd favorite Roberto Bautista Agut 7-5, 4-6, 6-3 by winning the final three games in a match that lasted almost three hours.