Both Serena Williams and Rafael Nadal began their French Open with straight-set victories against overmatched foes on Monday, while fourth seed Daniil Medvedev was stunned by Hungary's Marton Fucsovics in the first round.

Russian Medvedev, a runner-up at the 2019 U.S. Open and semi-finalist in New York this year, has yet to win a match at Roland Garros since his main draw debut in 2017.

Nadal of Spain embarked Monday on what he has described as his "most difficult ever Roland Garros" while Williams launched another attempt to clinch an elusive 24th Grand Slam title on her least successful surface.

Nadal, the undisputed king of clay, began his attempt to pull even with rival Roger Federer for the most by a man, 20, by beating Egor Gerasimov of Belarus 6-4, 6-4, 6-2.

His 2020 debut at a place he's won 12 trophies did not change Nadal's view of things at this pandemic-postponed event: It's colder than usual, the balls are heavier than usual, and he's had less preparation than usual.

"The conditions are completely different," he said, "than any other Roland Garros that we played."

"The ball is completely different. It is super slow, heavy. It's also very cold, slow conditions."

"I really believe that the organization needs to take a look at that for the next couple of years, for the health of the players, too, because the ball is super heavy and becomes dangerous for the elbow and for the shoulders," said Nadal.

In women's singles, China's only player Zhang Shuai eased into the second round for the fifth time in a row after defeating the 12th seed Madison Keys of U.S. with a 6-3/7-6(2) victory on Monday, while American Serena Williams is playing at Roland Garros for the 18th time, having made her debut in Paris in 1998.

Williams has returned to action still dealing with the lingering effects of an Achilles injury sustained in her U.S. Open semi-final loss.

The former world number one skipped the Rome tune-up event as a result but is confident of making a challenge for a fourth Roland Garros crown.

"I wouldn't be playing if I didn't think I could perform," said Williams, who turned 39 on Saturday.

"I'm not at 100 percent physically. But I don't know any athlete that ever plays physically when they're feeling perfect. That's just something I think as athletes we have to play with."

After she played OK in the opening set, then was terrific in the second, of a 7-6 (2), 6-0 win over 102nd-ranked American Kristie Ahn, Williams – so used to being questioned about court – was asked on this day about Nadal and Federer.

"I don't get involved in the 'greatest' talk. You know, the greatest for me is, and will always be, Jesus, so I'm going to leave it at that," Williams began.

"Rafa, I'm obviously a huge fan of his. I always have been. But it's like you can't compare two people that are equally great. Roger, I mean, he's Roger Federer. I think that says enough," Williams continued. "So, you know, it's like I don't understand why people want to pit, 'Who's this? Who's that?' They both have spectacular careers that 99 percent of people can only dream of and ... every single credit and every single thing that they get, they absolutely deserve it. I'm a big fan of both, to be honest."

(With input from agencies)