PARIS — For decades, the red clay that makes the French Open unique among Grand Slams has served as a gorgeous canvas for the game’s most artful practitioners, looking more like velvet than crushed brick under the Parisian sun.

But from Mallorca to Miami, clay courts of similar composition have served as the ideal classroom for grooming future champions.

Hard courts may dominate the U.S. tennis landscape, but clay, many coaches and pros believe, is the best surface for learning and mastering the game because of the range of skills and qualities it demands. Among them: fitness, balance and agility; a variety of shots and the smarts to know when to use them; a strategic plan rather than rapid-fire reflexes; and, above all, patience.

“It awakens your tennis IQ; that’s what I would say,” says coach Jose Higueras, a former Spanish player who joined the U.S. Tennis Association’s player development staff three decades ago and now advises coaches. “Obviously, if you learn how to play on clay, it teaches you better strategy. The surface forces you to build the points; you cannot get away with a big serve, because the ball is going to come back. It forces you to actually develop a strategy, better movement and better concepts.”

That’s why, for the most part, players reared on clay — such as Roger Federer, Rafael Nadal, Chris Evert and Martina Navratilova, with 73 Grand Slam singles titles among them — find it easier to adapt to hard courts than hard-court players faced with adapting to clay.

Much like a foreign language, clay-court fluency is more easily achieved at a young age.

For Americans reared on hard courts, which reward power above all facets of the game, acclimating to clay can be awkward. Big serves get robbed of their punch. Without understanding the art of sliding, timing shots is tricky. Moreover, even the most explosive player can’t abruptly change directions on clay; a simple cutback requires a degree of forethought.

Over the past 63 years, only three American men have won the French Open: Michael Chang (1989), Jim Courier (1991-92) and Andre Agassi (1999). Chang and Courier owe a debt to Higueras, who helped prepare them for the red clay three decades ago.

“It was definitely a very big learning curve, understanding how a ball bounces on clay,” Chang recalls. “I didn’t know the best way to play on it; I’d play on it like a hard court, and when I did that, I’d get in trouble because I’d be out of position.”

Higueras helped Chang, then 17, understand what shots he could hit that would hurt his opponent and what (defensive) shots he could hit when he was in trouble, so he could buy time to recover.

American women have had more success on clay during the same 63-year span, with eight claiming a total of 17 French Open championships since 1955.

Chris Evert, the queen among them with seven titles at Roland Garros (1974-75, 1979-80, 1983, 1985-86), learned to play on green clay in Florida at Fort Lauderdale’s Holiday Park, where her father, Jimmy, was the tennis director for decades.

“You learn how to construct a point better on clay,” Evert explains. “It takes thinking ahead. It’s like a chess match, thinking ahead maybe a shot or two: ‘If I drop-shot now, she’ll pull in.’ And you better be fit enough to hit 12 or 13 shots instead of three or four. It takes fitness and patience to win a point on clay.”

This year, of the eight American men in the 128-player French Open field, seven lost in the first round. Taylor Fritz was ousted in the second.

But three American women — Sloane Stephens, Madison Keys and Amanda Anisimova — reached the quarterfinals. Keys and Anisimova play matches Wednesday for semifinal spots.

The red clay at Roland Garros — actually finely crushed brick — is regarded as the slowest of all tennis surfaces. In truth, there’s not a huge amount of clay involved.

Picture each court as a three-layer cake that sinks 2½ feet into the ground. The bottom layer is crushed gravel. The middle layer is coal residue. The top layer is white limestone. And the clay, spread at a depth not much thicker than a dime, is the frosting.

Maintaining the French Open’s 15 match courts and 13 practice courts is a high-maintenance proposition involving 100 workers. Each morning, they uncover and sweep each court. After each set, the courts are swept, and the lines are brushed. After each match, the courts are swept, brushed and watered. And at day’s end, they are watered intensely and covered for the night.

As for the clay courts’ effect on players, on one hand, they demand greater fitness because matches tend to last longer. But on the other, they are easier on joints, ligaments and the body in general.

Explains sixth-ranked Stefanos Tsitsipas, 20, who played exclusively on clay as a youngster in Greece: “I personally think clay is the best thing if you have kids. Learning tennis on clay is very good for your body, for your development. It’s a way to learn how to slide, to learn the basics of tennis.”

That’s largely why the Evert Tennis Academy in Boca Raton, Fla., which prepares promising juniors for college or the professional tour, starts its young players on clay.

The academy has an equal number of hard and clay courts (15 each). When the juniors are 15 or 16, they’re shifted more to hard courts because that’s the primary currency of college tennis and the pros.

Regardless of age, Evert Tennis Academy players coming back from an injury are assigned to clay courts for two or three weeks before resuming work on hard courts.

Like Tsitsipas and nearly all ­Europeans, Andrea Petkovic learned to play on clay. It will always be her preferred surface, she explains, because of its familiarity and greater mental challenge.

“I like clay because it makes the game a little slower, and it gives you the opportunity to really use your brains and use tactical choices,” says Petkovic, a German who speaks four languages, writes occasional newspaper columns and is completing a book manuscript. “On grass and on hard courts, everyone has gotten so powerful, and tennis has gotten so quick, sometimes it’s more a survival than really what I consider playing tennis — which is like chess, in my eyes.”

Tsitsipas, a cerebral player who split clay-court matches with Nadal, regarded as the King of Clay, in Madrid and Rome in the run-up to the French Open, is drawn to clay for much the same reason.

“Clay courts require patience more than any other surface and the right strategy,” says Tsitsipas, who was edged Sunday at Roland Garros by 2015 French Open champion Stan Wawrinka in an exceptionally played 5-hour, 9-minute match over five sets. “If you’re playing the wrong way, and your opponent can dictate what you’re doing, then you’re screwed. . . . So [on clay], there is plenty of time to think.”

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