At what point is tall too tall?

NEW YORK -- Tall people, the studies insist, tend to be more successful than the rest of us.

According to a 2009 report in Australia's Economic record, men who are 6 feet or taller make an average of nearly $1,000 more per year than those who are 2 inches shorter.

"Taller people are perceived to be more intelligent and powerful," the study said.

It's true in tennis, too. Being tall -- to a point -- is a huge advantage. Social Darwinism, survival of the fittest, is a thread that runs through every match here at the U.S. Open.

On Wednesday, 6-foot-9 John Isner made that emphatic point in defeating Xavier Malisse 6-3, 7-6 (5), 5-7, 7-6 (9). Isner's blistering serve was the difference in those tiebreakers. One of his serves traveled 143 mph, the fastest of the tournament so far. His best second offering was clocked at 127, which would place him 35th fastest among male players, 1 mph ahead of some guy named Federer.

How important is Isner's serve to his game?

In a private postmatch interview, the question prompted laughter.

"Yeah," he said eventually. "Pretty important. Obviously."

Truly, size matters.

The average height for the men's top 10 is 6-foot-2½ inches, with Isner and Juan Martin del Potro (6-6) being the tallest. David Ferrer (5-9) and Janko Tipsarevic (5-11) are the only two who don't measure up to 6 feet.

On the women's side, three of the top five in the rankings are 6 feet or better: No. 1 Victoria Azarenka (6-0), No. 3 Maria Sharapova (6-2) and No. 5 Petra Kvitova (6-0). No. 2 Agnieszka Radwanska is only 5-8, but she compensates by being exceptionally crafty and creative. No. 4 Serena Williams is listed at 5-9, but her explosive power allows her to play bigger.

Of course, height alone does not guarantee success. Ivo Karlovic, at 6-10 the tallest man in the history of elite tennis, lost in the first round here and has won only 11 more career matches than he's lost. Six-foot-3 Akgul Amanmuradova, the tallest listed active women's player, is in her 13th season as a professional and still looking for her first WTA-level title.

Such is the yin and yang of size versus raw athleticism. Nature has a way of compensating if you are blessed with too much of one thing.

Those gifted few who fall between the extremes tend to win a lot of matches. Serena Williams might be the best example. Roger Federer and Rafael Nadal are both 6-1 and Novak Djokovic is an inch taller. They all possess the ideal ratio of speed and size. They have won 29 of the past 30 Grand Slam singles titles, suggesting that in today's physical game exceptional movement generally trumps power.

Del Potro, a serious freak of nature, is the one who interrupted that streak.

Not only is he the only non-member of the big three to break through (with a sublime performance here in 2009), the 182-pound Argentine is the tallest Grand Slam titlist in history. He is not exactly quick, but he moves well for a man so long. His big serve and forehand keep points shorter, mitigating a lack of speed.

This was the modus operandi for Lindsay Davenport. She won three majors (in a narrow span of six) from 1998 to 2000. Davenport says that Venus Williams is actually 6-3, but when they've stood next to each other, she's a tad taller. That would make Davenport, an analyst here for Tennis Channel, the tallest women to win a major title.

"I was not a good athlete," she said, smiling. "I couldn't cover the court. Venus … Well, in a sprint, it would be a tight one. Seriously, not even close. But you learn to compensate, take advantage of your strengths."

And mask your weaknesses. This is something Isner and del Potro each do quite well.

Isner, for example, leads the ATP World Tour with 870 aces, already more than last year's total of 811. He is second to Milos Raonic in frequency, with 15.3 per match. Against Malisse, Isner had 20 aces, but he also hit 57 serves that were not returned. So, 77 of Isner's 138 serves did not require him to run a step, and yet he won the point. There were also a number of occasions when one big serve left him with a simple groundstroke (usually the forehand) into the open court. In this way, he limited his disadvantage in the mobility department.

Sports, invariably, can be reduced to simple geometry. The better the angle, the better your chance for success; the longer the drive in golf, the better the angle to the pin and the more loft you can employ with a shorter iron to land the ball softly (hopefully, closer) to the pin.

Kevin Anderson of South Africa is 6-8 and Wednesday he met No. 4 seed David Ferrer, who is 5-9. This was a classic example of size versus movement. And despite a wide disparity in talent, Anderson hung tough, losing 6-4, 6-2, 7-6 (3). His serve (he topped out at 135 mph) kept him in it.

"The angle really helps you," Anderson said afterward. "You can go for more. I try to get the ball [bouncing] up on opponents.

"It's [movement] something I'm working on every day. I'm looking forward to putting the serve together with a sprint from the baseline. But in the end I know I'm going to rely on my serve."

OK, let's break it down:

The server stands 57 feet from the net, which is 3-foot-6 at the outside posts and 3 feet high in middle. The service box he's aiming for is 21 feet by 18 feet. So he's got 378 square feet to work with, trying to strike a ball with a 2.63-inch diameter and weighing 2 ounces as high as he can off the ground. Why? The higher the point of contact, the better the angle -- and, thus, a wider margin for error.

Thanks to the folks at Hawk-Eye, who brought you the on-court replay, we can tell you very precisely where players strike the ball. In his first-round match, 6-foot-6 Sam Querrey's highest contact point for a serve was 9 feet, 10 ½ inches off the court. The 6-5 Tomas Berdych managed 9-9. On Wednesday, del Potro and Anderson both cleared 10 feet -- barely.

Isner is in a completely different category. Against Malisse, his highest point of contact on serve was a staggering 11 feet, 11/16 of an inch above the court.

"Oh," Isner said when he heard the number, "that's nice."

And then he started doing the math with his fingers in the air.

"Let's see, I'm almost 7 [feet], and then there's my arm and the racket's 27 [inches]," he said. "So that means I'm jumping 2 feet in the air, right?"

More like 3 or 4 inches.

"Oh," he said. "I wasn't aware of the physics of it, but I am aware of the advantage it gives me."

In basketball parlance, Isner's playing way above the rim.

"It's a lot like basketball," Davenport said. "It's easier to get the ball in the basket when you're looking straight across at the rim, not from below. Look at [5-6 Olivier] Rochus or Michael Russell [5-8]. They have to hit up on the ball to get it over the net. It's common sense: If you're hitting down, it's a lot easier."

Isner knows this. His whole game plays off his serve. The rest of his game is just good enough to help him get into situations where he can exploit that service advantage. Sometimes it takes awhile; Isner has played two of the four longest matches in Grand Slam history. He has appeared in an ATP World Tour-leading 50 tiebreakers this year -- 17 more than next-highest Philipp Kohlschreiber. Izzy is 36-13 and will almost certainly set an ATP record for tiebreak wins.

The consistent power of Isner's serve can be mentally wearing. There were times when the ball hadn't even caromed off the back wall when Malisse would slump his shoulders, grimace and start walking to the other side. After a 132 mph bomb in the first set, his racket surrendered; broken strings are a common feature of Isner matches.

According to the ATP World Tour media guide, Isner is 6-9. Reliable reports, however, place him a shade over 6-10. This falls a bit out of the Federer-Nadal-Djokovic ideal range.

What if Isner were shorter? What if he were, say, 6-6? Would his slightly shorter arms allow him more flexibility and allow him to return serves better? Could he pull the trigger quicker on groundstrokes? Would he cover more ground with faster, shorter strides?

Would he be a better player?

"I don't think so," Isner said upon reflection. "My serve wouldn't be as good. My movement? Probably not that much better.

"If I had to guess, I would say no. I'll keep it like it is."

In other words, like all those tall guys of the world, he's not going to give an inch.