At any given time during John Isner's pro career, the hard serving American could look up at the ATP World Tour rankings and find some combination of Roger Federer, Rafael Nadal and Novak Djokovic.
Throw in two-time Grand Slam champion Andy Murray or, more recently, 2014 Australian Open winner Stanislas Wawrinka, and real estate atop the ATP rankings has generally been spoken for.
But as Isner celebrates the seventh anniversary this week of his 2007 pro debut here in Washington, he does so with the belief that the margin between the top players and the rest of the field is, at long last, beginning to narrow.
"I think that's the general consensus around the ATP, in the locker room a little bit," Isner said ahead of his opening match at the Citi Open from the William H.G. FitzGerald Tennis Center in Rock Creek Park.
"Those guys, especially the top 3 in the world, they're not going to go away, but I think that the gap has maybe closed a little bit."
Isner, the highest ranked American at No. 12 in the world, is not alone among the top seeds at the Citi Open who view the hard court season as an opportunity to earn valuable rankings points and to potentially inch closer to the elusive top 5.
Isner, though, wasn't able to capitalize on the opportunity himself as he lost his opening match Wednesday to Steve Johnson, 6-7(5), 6-3, 7-6(6).
Djokovic and Nadal have occupied the top two positions all year, with Federer a distant third, followed by Wawrinka and Tomas Berdych. Murray, sidelined earlier this year after back surgery, has dropped to No.10.
"I think there's a big opening," said world No.7 Milos Raonic, seeded second in D.C. and coming off a quarterfinals appearance at the French Open and his first career Grand Slam semifinal at Wimbledon.
"The biggest threshold and the biggest barrier or wall to pass is the one that Novak and Rafa have on the 1-2 spots. But I think that the rest of the parts, this year specifically, are up for grabs."
Raonic, who was been ranked as high as sixth in the world, and world No. 9 Grigor Dimitrov are both 23 years old and are the only top 10 players under the age of 25.
Raonic and Dimitrov, along with 11th-ranked Kei Nishikori of Japan, have been prominently featured by the ATP in marketing 'the next generation' of Grand Slam champions. All three were scheduled to play in this year's Citi Open, before Dimitrov withdrew due to illness. Raonic advanced to the third round with a straight set winover American Jack Sock, 7-6, 7-6, on Wednesday.
"The ATP has really touted those players," said Citi Open tournament director Jeff Newman, "as the three players who can take the torch from what has really been the 'Big Three' or 'Big Four' for so many years."
Djokovic, Nadal and Federer have combined to win 34 of the last 38 Grand Slam men's singles titles, with at least one of the three participating in each of those championship matches. Not since Marat Safin beat Lleyton Hewitt in the 2005 Australian Open has a men's Grand Slam final been void of one of the Big Three.
Nearly a decade later, though, Hewitt admits that a young crop of players could soon represent a changing of the guard.
"You can't expect Roger and those guys to keep holding it up forever," said Hewitt, playing in Washington this week for the seventh time in his career.
"Those younger players [Raonic, Dimitrov and Nishikori] have a definite chance. They've already performed well on the big stage — in Grand Slams and in Davis Cup ties. They're quality players and really it was only going to be a matter of time before those guys stood up."
Nishikori, seeded fourth in D.C., is enjoying his best ATP season to date, complete with titles in Memphis and Barcelona and a 32-8 record heading into the Citi Open.
He is also the only player outside of the top 4 to have reached the finals this year of a Masters 1000 event — the ATP's highest caliber tournament outside of the Grand Slams.
"I'm happy to be in this ranking situation [but] my goal is not the top-10. I'm trying to go further," said Nishikori. "I hope I can make another big step... Last year I didn't do too well in these [summer] months so it's a very important few months for me."
A new partnership with coach Michael Chang has Nishikori, 24, believing that he is now better prepared for deep runs at the upcoming Masters events in Toronto and Cincinnati and at the final Grand Slam of the year, the U.S. Open.
There is also that small matter of beating the top players — Nishikori is 0-7 against Nadal and a combined 3-3 against Djokovic and Federer.
"I think there's still a difference between the top-5 guys compared to the rest of the top-20 let's say ... But for me, I don't have any fear to play them anymore."
Nishikori advanced to the third round with a three-set win over American Sam Querrey (6-4;5-7;6-4) on Wednesday.
Confidence may readily available at the start of the hard court season, but consistently beating U.S. Open champions Djokovic, Nadal and Federer and joining them atop the world rankings is entirely different.
"It's really tough [to crack the top four]. It's hard to explain with better words," said Berdych, the top seed at the Citi Open and fifth ranked player in the world, who is a combined 11-45 lifetime against Djokovic, Nadal and Federer.
"I would basically say you need to win a slam to get there because the other guys are going to have at least one. If you want to be part of that, you really need to get [a slam].
"If there's a recipe to do it, I would like to know it. We're all trying."