A lot of superstition and thought go into choosing the right tennis ball. (John G. Mabanglo/EPA)

Before each serve on the ATP and WTA tours comes a weighty choice. Three balls sit in a pyramid on a player’s racket, or two ball boys offer two balls each.

To the untrained eye, those balls don’t seem to differ — at least not enough to merit the long seconds of consideration by choosy players, who examine them point after point.

But professional players know better. Any point can affect a given match, which can affect a season, which can affect a career. Their fates lie in those balls.

Some players choose better than others — or so say their serve percentages — but there’s no standard criteria. Superstition and ritual often outweigh logic.

American Donald Young, for example, doesn’t know which of the three balls will serve him best, but instinct has warned him for about a year now it won’t be the ball on the right. So he keeps the ball on the left and the ball on top and knocks the other one back to the ball kid.

“I don’t know why,” Young said. “It’s just a ritual, I guess.”

Svetlana Kuznetsova, on the other hand, knows it’s silly to believe the way a ball is handed to her has anything to do with the outcome of a serve. She knows it’s all about where it’s handed to her.

When Kuznetsova receives a ball from a spot behind the baseline and that ball performs well, she returns to that spot again and again. The ball kids on the other side of the court are reduced to spectators.

“I don’t know why,” Kuznetsova said. “But I’ve been doing it awhile.”

Richard Gasquet knows there’s only one right ball, but it only presents itself after he wins a point. He has no choice but to use that ball again. During his Citi Open semifinal earlier this month, the match stalled while the Frenchman asked a fan to hand a would-be souvenir back to him; he had won the previous point with it.

“I keep the same ball when I’m winning the point,” Gasquet said. “Everybody knows that about me. I’m always doing the same.”

Gasquet’s not alone in sticking to a winning ball, so the ball kids have a system: They hold the ball used in the most recent point down with one arm and another ball up in the air with the other.

Devoid of such trust in a proven winner, other players rely on physics. The smoother a ball, the faster it will travel, so many players seek out balls with less “fluff,” or puff on the felt covering, to reduce drag. The more fluff, the more air resistance, which slows it but increases spin.

“I like to serve my first serve with a ball that’s less fluffy. That way it will go faster,” Marina Erakovic said. “My second serve, I like to get a little more spin on it, and if it’s fluffier it will grab more. So I like to take a fluffy ball, a less fluffy ball, and the third one I throw out.”

For sixth-ranked Milos Raonic, one of the game’s most feared servers, spin is less important than pure power.

“I look for the smallest balls that will go the fastest,” Raonic said at the Citi Open.

Tournaments sign sponsorship deals with ball companies, so the brand can vary week to week. But are some balls really smaller than others?

“There would be no variation in the size of the ball,” said Jeff Ratkovich, Penn’s senior business manager for tennis balls. “Players are creatures of habit to the ultimate and see things. They’re so keenly aware of things — almost beyond what’s really there.”

What’s really there is a hollow rubber sphere 6.7 centimeters in diameter pressurized to about 12 pounds per square inch. That’s why tennis ball cans pop when you open them: The pressurization must match to keep the balls fresh.

As balls smash against the ground, the side that makes contact is pushed inward. The internal pressure pushes the side back out and propels the ball off the court. The more a ball is used, the less pressurized it becomes.

U.S. Tennis Association and International Tennis Federation rules say a regulation ball must bounce between 53 and 58 inches when dropped from a height of 100 inches. If you drop a tennis ball from your head and it bounces to your belly button, it’s good to go.

Balls are covered with a layer of felt, whose durability is determined by the surface on which the ball will be used. Hard-court balls tend to have extra-duty felt to withstand the abrasive courts, though women at the Citi Open played with regular duty Penn balls because they travel faster. To keep up ball pressure and reduce the effect of wear, ATP and WTA tournament balls are changed out seven games after warmups, then every nine games after that.

While a ball can wear and change throughout a match, the blueprint hasn’t changed much over the past few decades, according to Ratkovich. Perhaps the most noticeable change came in 1972: the shift from white to the ubiquitous “optic yellow.”

Studies have shown the optimal color is orange, which is most visible on all surfaces and against most backgrounds. But orange balls don’t show up well on television, so when the game was growing in popularity, the ITF approved the second-most visible color — “optic yellow” — for use in tournament play.

The U.S. Open will use Wilson balls this year and has since 1978. Ratkovich said the difference between the most prevalent tennis ball brands is minimal, but there will be a difference between the Penn balls used elsewhere in the U.S. Open Series and the Wilsons in play at Flushing Meadows.

“They’re made in two different factories. They’re actually made in different countries,” Ratkovich said. “They don’t share their recipe with us, and we don’t share our recipe with them. . . . What we equate it to is baking a cake in one country and baking a cake in another. Even though you have the same ingredients, they’re just going to taste a little bit different.”

You may not notice the difference, but the players will, and they will choose their service balls accordingly. After all, a Grand Slam title may depend on the decision.