MANY have come and gone without making a dent. Others are still bashing away trying to force their way through.
For all their promise, those "next big things" of men's tennis have been unable to penetrate the incredible barrier that the absolute elite have created.
Take, for instance, Bulgaria's Grigor Dimitrov, who with a playing style likened to the great Roger Federer, and two grand slam titles as a junior, was expected to become a force on the ATP tour.
Though he reached a world ranking of No.8, the career of "Baby Fed" has been reduced to a crawl, his best result at a grand slam remaining the semi-final appearance at Wimbledon in 2014. Now 25, he's dropped to No.39.
Then, among numerous others, is our own Bernard Tomic, who Federer said in 2011 was "on the brink of doing great things" after reaching the quarter-finals of Wimbledon in 2011.
As it stands, that result remains his "greatest thing" - his best result at a major. The 23-year-old's ranking has so far peaked at No.17. He's now two places back.
And so, still we wait for the next young star to really announce themselves on the big stage - just as a 21-year-old Federer did at the All England Club in 2003, or Rafael Nadal at Roland Garros in 2005 at 19, or Novak Djokovic at Melbourne Park at 20 in 2008.
Of course, throw in Andy Murray and the "Big 4" have won 43 grand slam titles out of the last 48 with Stan Wawrinka claiming two and Marin Cilic, Juan Martin Del Potro and Marat Safin one each.
Their dominance - even now they hold the top four rungs on the ATP tour rankings - has meant tennis has not had a grand slam champion under the age of 23 this decade.
There was seven in the 1980s, and eight in the 1990s and 2000s, the last being Del Porto at the US Open in 2009.
Part of the next wave of young challengers that includes another Aussie, Nick Kyrgios, Austria's Dominic Thiem will be aiming to become the first in 2010s.
The 22-year-old has risen to No.8 in the world after clinching four titles this year - the most of any player bar Djokovic (six) - and becoming just the ninth active player to win crowns on three surfaces in the same year.
After making the French Open semi-finals last month, he claimed his first title on grass at the Mercedes Cup, beating Federer in the semis and Philipp Kohlschreiber in the final.
It was the second time in a row he had defeated Federer and came after a win over Nadal to claim the Argentina Open on clay in February.
"For sure, Djokovic and Murray, and also the other two, they have a couple more very good years left," said Thiem, one of just five players under the age of 23 in the top 50. There is, in contrast, 21 players aged 30-plus.
"The goal for the young players, also me, has to be to compete with them at their peak. There's nothing better than that level."
And "for sure", Djokovic - his conqueror in the semi- finals in Paris - is at his absolute peak, and standing in the way of not only Thiem, but every player on the tour.
The Serbian destroyer is gunning for a 13th grand slam title - to move within one of Nadal and Pete Sampras - and a fifth in a row. Only American Don Budge has more (six from 1937-38) in succession.
The 29-year-old felt relief when he claimed a first French Open title, but has now set his sights set on becoming the first man since Rod Laver (1969) to win a calendar-year grand slam by adding more Wimbledon and US Open crowns.
''We're moving on," he said. "It's back on grass now and starting from scratch. One thing we all learn in tennis is to reset a day or a week later. That's the sport we are in. We don't have too much time to reflect on what we have achieved."
While youngsters such as Thiem and Canadian Milos Raonic are a clear and present danger, Djokovic's greatest rivals, Murray and Federer, remain at the head of the queue when it comes to greatest challengers.
Though he's lost to Djokovic in 13 of their past 15 meetings, including in this year's Australian and French Open finals, Murray has made the finals of his last four events, winning in Rome (on clay) and at Queen's (on grass) for an unprecedented fifth time.
"I'm pretty sure I wouldn't have done that before," said the 29-year-old Scot. "It's a sign things are going the right direction the last few months."
Federer, 34, meanwhile, still hungers for an 18th grand slam title - and in particular a record eighth Wimbledon crown - after going down to Djokovic in the final the past two years.
"Wimbledon is the holy grail," he says.
That, and the fountain of youth.
Aces up their sleeves
IT'S fashionable to have a great in your corner. Andy Murray has regained the services of Ivan Lendl, Milos Raonic has hired John McEnroe and Stan Wawrinka has added Richard Krajicek. Michael Chang coaches Kei Nishikori and Boris Becker guides Novak Djokovic. "Let's face it, we do understand the game probably more than most, so everybody benefits," Becker said.
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