Rafael Nadal of Spain returns a shot during the men's singles 4th round match against Maximilian Marterer of Germany at the French Open Tennis Tournament 2018 in Paris, France, on June 4, 2018. Rafael Nadal won 3-0. (Xinhua/Luo Huanhuan)

PARIS, June 4 (Xinhua) -- Men's world number one Rafael Nadal and his female counterpart Simona Halep won in straight sets to secure their places in the quarterfinals at the 2018 French Open on Monday.

Despite conceding a break at the start, 10-time champion Nadal swept Roland Garros debutant Maximilian Marterer of Germany 6-3, 6-2, 7-6 (4).

"6-3, 6-2 have been very positive 12 games for me. In the third, I had the chance at the beginning to have the break and probably take an important advantage to close the match, but didn't convert it. Then I had a couple of mistakes with my serve and suffered a tough third set," said Nadal.

Nadal will next face Argentine Diego Schwartzman, who rallied from two sets down to eliminate No. 6 seed Kevin Anderson in full sets.

Halep, in pursuit of her maiden Grand Slam title in Paris, met little resistance from Belgian Elise Mertens and conceded just three games for a 6-2, 6-1 victory in 59 minutes.

"Even if you win with an easy score, if you lead many games ahead, it's not about that you already won the match, so you have to stay focused on every ball and every point. At this level, no one gives up at the beginning. You have to stay there for everything and to give everything at every moment," said Halep.

"It was not that easy as the score shows. She's a tough opponent. I had to pay attention to every ball that we played," the Romanian added.

Halep will take on Angelique Kerber in the quarterfinals. The German saw off home favorite Caroline Garcia 6-2, 6-3.