Steffi Graf's 1988 ranked as best season ever, Roger Federer's 2006 at No. 7

Steffi Graf's landmark 1988 season was selected as the greatest tennis season of all time by a panel of experts at Tennis Channel. However, what was surprising was how low Roger Federer's 2006 and Novak Djokovic's 2015 seasons were ranked in the top 10 list.

By all accounts, Roger Federer in 2006 had one of the best seasons on the pro circuit ever. He made it to the final of all four Grand Slams and won three of them, with his juggernaut only grinding to a halt at Roland Garros - against the King of Clay Rafael Nadal.

Federer lost just five times in the whole season and won a whopping 92 matches, in the process capturing four Masters titles as well. However, in the countdown run by Tennis Channel, Federer's memorable journey only came in at No. 7.

There can be little debate about the number one spot though, with Steffi Graf's Golden Slam season standing head and shoulders above the rest.

Steffi Graf

That year Graf became the only tennis player in history to win the four Majors as well as the Olympic gold; 1988 was clearly the German's annus mirabilis.

Novak Djokovic joins Roger Federer in the lower half

Novak Djokovic, the current World No.1

Novak Djokovic's 2015 run also surprisingly came in low on the list, finishing one spot below Federer. Djokovic went on a spell-binding spree that year, producing one of the greatest passages of play ever seen in the game.

The Serb won three Majors out of four finals reached, a record six Masters and the year-ending ATP Finals, in a year he remained number one throughout. Djokovic also dominated Rafael Nadal, Roger Federer and Andy Murray thoroughly that season, with a near-perfect display of his considerable skills.

It seems the panel of experts gave a raw deal to recent players, with even Serena Williams' 2002 coming in at a lowly 9th. Serena's achievements that year are considered to be at a different level altogether, as she won three Slams (and withdrew from the fourth due to injury) amid incredibly high competition.

Old is gold? Roger Federer, Novak Djokovic make way for greats from the 70s and 80s

The top six seasons in the list all feature players from before the 90s. Rod Laver's 1969 came in second, and Martina Navratilova's 1983 rounded out the top three.

Rod Laver At Wimbledon

Laver bagged all four Grand Slams in 1969 (for the second time in his career), and won 18 of the 32 tournaments he entered with a 106-16 record. Navratilova in 1983 won three Majors, as her newfound superiority in fitness gave her a distinct edge over her peers.

Margaret Court's 1970, when she won all the four Majors, was ranked fourth. But perhaps the most surprising entries are Jimmy Connors' 1974 at No. 5, and John McEnroe's 1984 at No. 6.

Connors won three out of four Majors in 1974, but didn't compete at the French Open - which automatically puts him below Federer and Djokovic at the Slams. And while McEnroe boasted the best ever men's win-loss ratio (82-3) in 1984, he couldn't win more than two Majors that year.

For fans of Roger Federer, 2006 will remain one of the greatest spectacles in tennis history, with his beautiful game running riot around the world. The Novak Djokovic fans, meanwhile, will argue that no one can top 2015.

As with any such list, the debate has only begun, rather than ended, with its release.

Here are all the 10 entries in order:

1. Steffi Graf, 1988
2. Rod Laver, 1969
3. Martina Navratilova, 1983
4. Margaret Court, 1970
5. Jimmy Connors, 1974
6. John McEnroe, 1984
7. Roger Federer, 2006
8. Novak Djokovic, 2015
9. Serena Williams, 2002
10. Monica Seles, 1992