NEW YORK (AP) Two 23-year-olds, Milos Raonic and Grigor Dimitrov, broke through to their first major semifinals at Wimbledon.
Perhaps this year's U.S. Open will be the tipping point for the rise of a new generation. But recent history suggests that if an outsider seizes on the trace of vulnerability in the ''Big 4'' to win in New York, it's more likely to be a veteran.
''We didn't have many young players who were able to challenge for top spots and win Grand Slam titles,'' Wimbledon champ Novak Djokovic said. ''So this is something that is happening now, but it's still a long way to the Grand Slam title. It's not something that can happen overnight.''
It was then-28-year-old Stan Wawrinka who snapped the streak of 16 straight Grand Slam titles by Djokovic, Roger Federer, Rafael Nadal and Andy Murray when he won the Australian Open in January. The only other men in the U.S. Open field who have reached a major final in the past five years are 32-year-old David Ferrer and 28-year-old Tomas Berdych.
The U.S. Open starts Monday with Djokovic, Murray, Wawrinka, Maria Sharapova and Venus Williams among the big names on the court. The player with the most impressive performance leading up to this tournament was a 29-year-old. Jo-Wilfried Tsonga, the runner-up at the 2008 Australian Open, beat Djokovic, Murray, Dimitrov and Federer to win the title at Toronto earlier this month.
As the sport has grown more physical, Grand Slam championships became less likely not only for teenagers but for players in their early 20s.
''Everybody realizes that you're reaching your peak physically maybe a little bit later and then they're staying there longer, because they have the technology and they're more systematic about their training,'' said Patrick McEnroe, the U.S. Tennis Association's general manager of player development.
So a group of men who aren't that young by tennis standards have gained little experience of playing in the highest-pressure moments. The oft-repeated stat is that the Big 4 have won 36 of the past 38 Grand Slam titles.
Contrast that to the five years before Nadal won his first major championship at the 2005 French Open to start that streak. As Pete Sampras' reign was ending and Federer's beginning, 12 different players won the 20 Grand Slam titles; for six of them, it would be their only major championship.
Now, it's daunting not just to win championships but to even get close to them.
Since Murray reached his first major semifinal at the 2008 U.S. Open, the Big 4 have hogged 63 of the 96 slots in the semis. And since the 2006 French Open, the first Federer-Nadal major final, they've filled 58 of the 68 spots in Grand Slam title matches. Nobody else reached a major final for 10 straight events from the 2010 U.S. Open to the 2013 Australian Open.
''It's definitely been a tough time for everybody else trying to break through,'' Raonic said.
Especially younger players. Of the eight other men to play in Grand Slam title matches since the 2006 French, only Tsonga and Juan Martin del Potro were under age 24.
''I was really impatient - I wanted things to happen quick for me, just wanted to achieve right way,'' Dimitrov said.
''I can't forget that nowadays the game has changed so much that nothing happens like that,'' he added, snapping his fingers.
A 20-year-old del Potro stunned Federer in the 2009 U.S. Open final, seemingly heralding the arrival of a new generation. It wasn't to be. Del Potro, now 25, has been hampered by injuries and won't play in New York this year because of a wrist problem.
He and his contemporaries are a glaring omission from the upper echelons of the sport. The rankings' current top 10 include the two 23-year-olds, Raonic and Dimitrov; no one else is under age 27.
Other promising players in their mid-20s such as Kei Nishikori, Ernests Gulbis and Marin Cilic have never maintained a consistent high level.
Djokovic and Murray were born a week apart in 1987; Nadal is less than a year older. If they can stay healthy - certainly a big ''if'' with Nadal, who's out of the U.S. Open with a wrist injury - the logjam at the top could stick for a while.