A step or two slower than they used to be, with families to take care of and with nagging injuries to nurse, the champions of a decade ago continue to light up the ATP Tour with as much fight, determination and sublime skill as ever.
As they come to the end of their playing careers, the tour's elder statesmen continue to battle through the long, arduous seasons, hoping to get their rankings back to a position where seeding might help protect them in the early rounds of tournament draws.
If they can manage that, their chances of recapturing their former glory increase significantly. And no one believes in them more than they do.
Still blessed with the same weapons and shot-making ability that propelled them to the top of the game, they are still a danger to any player at any event.
The current top four, or anyone else for that matter, never want to see the following names in their side of the draw at the Masters 1000 or Grand Slam events, and for good reason.
But to get back to where they enjoyed their best playing days, it takes a lot more than one or two shocking results—it takes a season's worth of consistent wins.
The top 10 is a very tough nut to crack, but the following players have all been there before and know what it takes to survive at the very top.
Can any of them perform at the level needed, and for the time needed, to make a return to the top 10?
These are the players who, in my opinion, have the best chance.
*All players are aged 29 or over and have been former Grand Slam/Masters 1000 event champions.
The 32-year-old is currently ranked 26th in the world but has been as high as No. 3 back in 2006.
The giant Croatian has a number of ATP titles to his name, including the 2010 Indian Wells Masters title.
He has also been a finalist at three other masters events.
The 6'4" veteran has the type of game that can trouble the best players in the world when he is on form. With a big serve and flat ground strokes, Ljubicic can hit clean winners from almost anywhere on court.
One of his biggest weaknesses is his movement.
He appears to be slightly sluggish against the better players and struggles when the points are long and physically demanding. If he wants to get back to the top, his fitness is key.
A lot depends on how much he desires to be back at the top. At 32, he will be well aware that his days as a professional tennis player are running out.
Most fans are aware of Lleyton Hewitt's impressive record, but the 30-year-old Australian has a lot of work to do if he wants to get anywhere near the top 10 again.
The tenacious Hewitt was ranked at No. 1 in the world at his peak in 2001. He has won some of the biggest and most prestigious events in the world on multiple occasions and has helped his country win the Davis Cup.
As well as being a Wimbledon and US Open champion, he also has two year-end Masters Cup trophies in his collection.
Currently ranked at 199 in the world, Hewitt has suffered badly with injuries in the last few years—injuries that have hampered any attempt at a return to the top echelon of men's tennis.
Two hip operations, as well as a foot operation earlier this year, have prevented Hewitt from re-finding the form that took him to the top.
There is some doubt as to whether Hewitt will continue playing past the current season, especially if his injury woes continue to trouble him.
His fiercely competitive nature means you can never count him out until he decides to hang up his racket.
But with a growing family to look out for and recurring injuries to play through, his chances seem to be diminishing.
Juan Carlos Ferrero, nicknamed 'The Mosquito' by fellow players due to his speed around the court, is currently ranked 83rd in the world rankings.
The 31-year-old Spaniard has created a legacy that will not be forgotten.
In 2003, he reached No. 1 in the world rankings after winning the Madrid and Monte Carlo Masters, as well as his only Grand Slam title at Roland Garros.
When he is injury free and match-fit, Ferrero's game can still be a handful for anyone on the tour. His aggressive baseline game is still devastatingly effective, and his agility around the court makes him a very difficult player to put away.
In 2010, he showed the world he is still capable of the same level of play that won him a Grand Slam. After winning two ATP titles back-to-back, he stated that his goal was to "get back to the top 10."
If he is to achieve his goal he must stay fit and injury free. If his body can hold up to the rigours of a full season on the tour, then he has the game to make it happen.
Reaching a high of No. 3 in the world in 2006, David Nalbandian's career has been very good, if not great. The Argentine is currently ranked 64th in the world after a 2011 plagued by injury.
The 29-year-old was the winner of the 2005 Master Cup and also has both the 2006 Paris and Madrid Masters titles to his name.
As one of the heavyweights of the game, Nalbandian has always struck fear into his opponents with his aggressive play and vast array of shots.
He has not enjoyed the best of seasons on tour due to a hamstring injury and a hernia, which forced him to miss a number of events.
Since his return, he has struggled to find the form that used to win him tournaments, although if he can gain some much-needed confidence, he could well be pushing for the top 10 again in the future.
As one of the most consistent top 10 players in recent years, Nikolay Davydenko now finds himself occupying No. 34 in the singles rankings after a slightly disappointing year.
The 30-year-old Russian has had an outstanding career—one which peaked in 2009 when he won the year-end Masters cup event in Shanghai.
He has never won a Grand Slam but has three Masters titles under his belt and a host of other tournament wins.
Davydenko's game is built around measured aggression. He prefers to control points from the baseline, working his opponents from side to side—a strategy that has worked for him over a long period of time.
2011 has seen a drop-off in performance for Davydenko, with the Russian's only success coming at Munich, where he took the title.
A lack of belief and confidence could be to blame for his loss of form, but with a few wins and a bit of luck, it would be no surprise to see him back near the top 10.
Andy Roddick, the former world No. 1, has managed to keep a consistently high ranking since breaking onto the scene as a teenager.
Roddick has a number of Masters Series titles to his name, as well as the 2003 US Open title. He has been a Wimbledon finalist an astounding three times and America's best player for the majority of his career.
The explosive American has had to endure a lot of criticism of late, but the fact he is still ranked at No. 15 in the world (the highest-ranked player on this list) shows that he is still a highly dangerous player.
The big-serving Roddick is a threat for very obvious reasons. It is the obviousness of those reasons, however, that his critics have latched onto as weaknesses.
Maybe it is a little harsh to describe his game as one dimensional, but it is true that he lacks the variation that might allow him to beat the current top four—something he has struggled with in recent years.
He has never been afraid of hard work and if he can bring all the elements of his game together at the same time, I believe he can become a top 10 player once again.