Growth in Tennis? Tape Measure Is Telling At 6-10, John Isner, left, is among the tallest players in the men's game, but he didn't stand far above Juan Martín del Potro at the Western & Southern Open. One recent breezy evening in Montreal, Juan Martín del Potro traded powerful serves and thunderous forehands with Milos Raonic for two otherwise uninspiring sets, won by Raonic. This tale of tall tennis players highlighted what many have contended - and in some cases feared - will be the future of men's professional tennis. In another setting - a basketball arena, for instance - del Potro, at 6 feet 6 inches, and Raonic, at 6-5, would have stacked up as average-size competitors. On a tennis court measuring 78 feet long by 36 feet wide, they looked a little out of place, even against each other, like neighboring apartment towers hovering over a quaint suburban village. Raonic's new coach, Ivan Ljubicic, said that was only because longtime followers of men's tennis had been conditioned to watching smaller or more average-size men compete. But the trend toward taller players is indisputable, he said, while stopping short of proclaiming the sky as the limit. "I don't think the tour will become a 6-7, 6-8 tour," Ljubicic said. Yes, if you are that size, it could be an advantage, but tennis, I think, will be more about 6-5, where you can make the most out of the height without giving up too much in the other areas. And if the tall guy can move really well, then you have something special. Ljubicic, a 6-4 Croat who retired in 2012 after 14 years on tour, was an example of the sport's growth spurt. As further proof to support his argument, he cited Croatia's 2005 Davis Cup championship team, which included Goran Ivanisevic (6-4), Mario Ancic (6-5) and Ivo Karlovic (6-10). Echoing Ljubicic, Ivan Lendl offered a generational arc from him to Andy Murray, the holder of the Wimbledon and United States Open titles. "When I came in, at 6-2, and there were people saying, "Well, he's too tall; he won't be able to move properly," " said Lendl, who turned pro in 1978 and is now Murray's coach. And now you have guys like Andy, who is 6-3 or 6-3 ½, and they move great. Tennis players have been getting bigger for years. When Lendl emerged as a force in the early 1980s, rare was the top-ranked man who was more than 6 feet. A decade later, Andre Agassi, at 5-11, and especially Michael Chang, at 5-9, were considered undersize overachievers. In those days, Boris Becker, at 6-3, contended that men's tennis was not only trending tall but would eventually be dominated by players well over 6 feet. While part of his prediction has not come true, it may be premature to say he was wrong. Heading into United States Open, 9 of the top 32 men's players were at least 6-5 - the tallest being Karlovic and the American John Isner, at 6-10. During this summer's hardcourt season leading into the United States Open, del Potro defeated Isner in the finals in Washington. Raonic, a 22-year-old Canadian, made the final in Montreal, where he lost to Rafael Nadal. Isner upset No. 1 Novak Djokovic in the quarterfinals in Mason, Ohio, and outlasted del Potro in the semifinals before losing in two tiebreakers to Nadal. "Every sport is going up and up," Lendl said. Look at basketball - and I don't understand basketball - but I do know that the guys who were playing center before are playing wings now, or whatever you call them. A trend does not necessarily become the rule, however. The Miami Heat won consecutive N.B.A. titles without a conventional center, and small, creative point guards have been in vogue for several years. In men's tennis, taller players have produced increasingly good results, but the very best or great players have been holding steady in the range of 6-1 to 6-3. Patrick McEnroe, a broadcaster and director of player development for the United States Tennis Association, argued that Roger Federer and Nadal, both 6-1, Djokovic (6-2) and Murray are and will remain the perfect fit for a game that demands the body stay low and coiled. "Tennis is a movement sport at the highest level, especially now with the technology of rackets and strings," McEnroe said. A male player from 6-1 to 6-4 is going to move much better in a confined space than someone who is 6-5 to 6-10. Obviously, ball striking is also of primary importance, but in a series of stop-start movements, give me the more agile and mobile player all day.