NEW YORK—Milos Raonic and Jerzy Janowicz are the twin towers of tennis’ future. The tower part is easy to see. Janowicz is 6’8”; in his hands, a Babolat looks as much like a toothpick as it does a racquet. Raonic is 6’5"; with his long legs and lanky frame, he appears to be taller than that. But the twin part of their relationship is almost as striking. While they don’t look or act anything alike, the two 22-year-olds could be long-lost, separated-at-birth brothers—one nice, the other...not as nice. Together they may extend two of the major trends in tennis of the last two decades: The rise in player height; and the rise of Eastern Europe to something close to dominance.

Janowicz was born on November 13, 1990 in Lodz, Poland; Raonic was born six weeks later, in Podgorica, Montenegro. From those beginnings, it’s easy to craft a narrative of polar opposites. Raonic’s parents are both engineers with advanced degrees, and he moved to Canada with them when he was 3. Janowicz’s parents were professional volleyball players who stayed in Poland; recognizing his youthful talent for tennis, they sold their sporting-good business when he was 11 to devote themselves to his career. While Raonic worked with Tennis Canada as a junior, Janowicz struggled for sponsorship money.

Raonic is quiet and composed on court; this is a young man who chose to play tennis as a kid because he could do it alone with his father and a ball machine. Between points, he lopes placidly and rarely deviates from his pre-serve rituals. He lulls audiences with his lion-serve/lamb-return game, which produces few rallies and little drama. Like his idol Pete Sampras, Raonic’s serve is so good that it not only puts a stranglehold on his opponent, it does the same to a match. Raonic respects and emulates today's top male players as well; you get the feeling that, more than anything else, he’s dying to be accepted into their tiny club. He has certainly mastered their style of safety-first press-conference answers. Asked today what he would consider a “good U.S. Open” for him. Raonic said, “I think if I do things well, I will give myself an opportunity to do things well.” I wonder what Ernests Gulbis would say about that stunning revelation.

At this year’s Australian Open, Roger Federer said that, of the current group of young guns, he thought Raonic was the most likely to succeed. It wasn’t so much because of his talent, but because of how well he has organized his off-court life. In a way, the assimilated Raonic, with one foot in North America and the other in Eastern Europe, is a logical star for this most international of sports. He speaks English and Serbian, roots for Real Madrid and the Toronto Raptors, and like all good stateless, financially organized pros, he splits the difference by claiming residence in tax-free Monte Carlo.

The high-strung Janowicz, by contrast, bellows when he hits the ball, walks with short, brusque steps between points, and appears ready to detonate at the slightest provocation. If Sampras is the behavioral antecedent to Raonic, Marat Safin appears to be Jerzy’s closest tennis ancestor. Today, frustrated by a bad back and a frugal opponent in Maximo Gonzalez, Janowicz blasted two balls deep into neighboring Corona Park. Later he tried an underhand serve and yelled at the chair umpire after a close call, “That was SO! OUT!” Off-court, Janowicz is one of the few men willing to publicly disrespect the Big 4; earlier this year he called Novak Djokovic a phony and Federer a snob. If you want an end to boring presser answers, Janowicz is definitely your man. Today, in his misery, he took out some of his frustration by railing at the local media for our “stupid questions.”

In the stands, Raonic’s mother and father watch with a polite lack of expression. Janowicz’s entourage, not surprisingly, isn’t as docile. They clap in unison after every point he wins and stand together in a show of strength at important moments. Their vocal support for Jerzy from the player’s box in Centre Court when he played Andy Murray in the Wimbledon semis shocked some in the audience that day. It felt like, now that we had gotten used to the Djokovics, it was time for a sequel: Meet the Janowiczs. We’ll surely get to know these enthusiastic hand-clappers better over the coming years.

(Of course, the narrative of opposites is just that, a narrative. Janowicz, who has a good sense of humor, is hardly the Drago of tennis, while Raonic, belying his nice-guy image, refused to admit that he had touched the net in winning a key point versus Juan Martin del Potro in Montreal, angering the Argentine.)

Raonic and Janowicz have taken different paths, and used different methods, but by this summer they had arrived at roughly the same place. Janowicz, who is currently ranked No. 14, made his first Grand Slam semi at Wimbledon. Raonic, currently at No. 11, reached his first Masters final in Montreal a month later. Yet the two don’t have a history of playing well at the same time. Just when you’re ready to call one of them the Future of Tennis, the other makes you think again. After Wimbledon, I thought Jerzy had passed Milos for good in the race to be the Next Big Thing. But I had to put those thoughts on hold again after Raonic’s runner-up finish in Montreal.

In case you’re wondering, Raonic and Janowicz have never played as professionals. When the U.S. Open draw was made on Friday, a meeting finally seemed possible; each was placed in the weak third quarter of the draw. But the Twin Tower Tussle, the Fight for the Future, will have to wait a little longer. While Raonic won his first-round match today, Janowicz, nursing a bad back—he said it felt like someone had stuck a knife in it—went out to the 247th-ranked Gonzalez in an unfortunate straight-setter.

Whatever their successes, neither player is a sure thing. Even in his win today over Italian qualifier Thomas Fabbiano, Raonic’s usual flaws were on display. He hit 28 aces to Fabbiano’s zero—that’s as close to an unfair advantage as you can get in tennis—but often failed to return the Italian’s sub-90-M.P.H. second serves. Raonic has modeled himself after Sampras, but this afternoon we were reminded of the wide disparity between the two. Where Sampras famously needed just one break to win a set, Raonic, shanking routine backhands wide and sending forehands 20 feet long, was unable to hold onto his single-break lead in the second set. Fabbiano, despite giving up eight inches, 165 ranking points, and 27 M.P.H. on his first serve, began to read Raonic’s delivery and eventually pushed the set to an 8-6 tiebreaker.

Janowicz has the better athletic pedigree, and he’s the better mover and all-around player of the two—if I had to guess, I’d say the future belongs to him. But Raonic has the cannonball, and as Federer says, he’s the more level-headed and mature presence. As a future star, Raonic wouldn’t have as many sharp edges for fans to accept as Janowicz, but Jerzy would be the more exciting and dangerous presence. He plays an explosive brand of tennis that would be an antidote to today’s defense-driven game.

Speaking of defense-driven games, the last two rivals to be so close in age are Novak Djokovic and Andy Murray, who were born a week apart in 1987. Can Janowicz and Raonic push each other and match their accomplishments? It’s a big ask. Today Raonic assessed his chances at winning a major and concluded, “It’s still a long ways to go, very long ways to go.”

(Janowicz, naturally, had a different answer to this same query at Wimbledon. Asked how good he could become, he paused, stared down at his fingernails, and finally said in his high-pitched voice, “You know, I really hate these kinds of questions.”)

A long ways to go: That may be the ultimate legacy of today’s top players. They’ve made the road to the top that much longer, the summit that much higher, the future that much farther away.