LONDON (Reuters) - Few subjects animate tennis aficionados quite like the "greatest of all time" debate, but there is a consensus that Rod Laver's 1969 calendar year grand slam remains a yardstick for the modern game.
But for a quiet revolution that took place on the Wimbledon turf two years previously, however, Laver's feat would be absent from the record books and tennis may never have flourished into the global spectacle it is today.
Fifty years ago, the traditionalism of the All England Club hardly appeared fertile ground for radical thinking.
But maverick chairman Herman David decided it was time to bring the professionals, then regarded by many as self-serving mercenaries, back in from the cold.
Thanks to David's "lightbulb" moment, a few weeks after the conclusion of the still staunchly amateur championships of 1967, eight pros were invited in through the gates to contest the "Wimbledon Pro".
Laver was joined by fellow Australians Ken Rosewall, Lew Hoad and Fred Stolle, Spain's Andres Gimeno and Americans Pancho Gonzales, Dennis Ralston and Butch Buchholz.
Enthusiastic crowds turned out for the four-day event, the BBC cameras rolled and, unthinkably, prize money totalled $45,000. The invasion of "big-time tennis" had begun.
"What Herman did was exciting and a brave move," Laver, 78, told Reuters in an interview.
"I think (Open tennis) was something people had been thinking about. The game was split and people were asking why did it have to be that way?
"A lot of those amateur officials must be turning over in their graves now thinking what a bad decision it was not to have started Open tennis earlier."
The event proved a great success as Laver, who also achieved the calendar slam in 1962 before leaving the amateur ranks, played as if he had never been away, beating Rosewall in the final.
"I thought the tennis was pretty amazing," Laver said. "And for me it just was unbelievable to be back.
"When I turned professional in 1963 I told myself I will never see Wimbledon again, nor the U.S. Open, the Australian, the French. There was no way I could live on amateur tennis.
"We had all won Wimbledons and been at the top in amateur tennis. We knew we would have a lot of history and trophies but that doesn't put food on the table. That's why we went pro."
The genie was out of the bottle. The shackles of amateurism fell away and the next year, following Wimbledon's audacious lead, all four grand slams opened to professionals.
David, inducted into the International Tennis Hall of Fame in 1998, hatched his plan after watching Laver win the World Professional title on the fast wooden boards of Wembley Stadium.
Laver recalls a conversation they had.
"He said you guys come and fill up Wimbledon at the weekend and you can come and play in our tournament next year," he said.
"I think he knew it had to be broken up. He knew amateur tennis wasn't the answer. I think he thought if the All England Club do it, it will force Open tennis.
"It was genius on the part of Wimbledon."
Laver's first match at Wimbledon for five years was against Stolle -- which he won 6-4 6-2.
"It was a thrill walking on to Centre Court, all the memories came flashing back," Laver said.
Stolle recalls it fondly too. "It was pretty special. I knew I was creating history," Stolle, who turned pro in 1966 after reaching the Wimbledon final in 1964 and 1965, told Reuters.
"Rocket (Laver) dispensed with me and I remember rushing back to get changed so I could watch my idol Lew play Pancho. I remember match point and Lew put a lob on to the baseline, chalk went everywhere. Pancho took a ball and smashed it over the stands.
"The next day Muscles (Rosewall) destroyed him."
Stolle believes the Open era should have happened sooner and that Laver, who won 11 grand slam titles, would have been way ahead of the 18 of Roger Federer had he not missed five years.
"We always thought it might come about but it always missed by a couple of votes," he said. "I think someone had to use the bathroom whenever they took the vote, that kind of stuff!
"Think of those slams that Rocket missed out on."
Ralston joined the pro ranks in 1967 having reached the Wimbledon final in 1966 when he lost to Manuel Santana.
He said the amateurs always knew the pros were superior.
"I knew they were better players, anyone that had any sense knew that," Ralston told Reuters. "I wanted to have a shot at playing against them and thankfully in '67 I could.
"Wimbledon had the courage to let those 'horrible pros' who were playing for money come in and play.
"It was a huge turning point... Back then we were happy to have anywhere to play. We had no clue the door was about to open, we were just happy, especially guys like Pancho, Rod and Muscles who had been away so long.
"Boy it was great to be back at Wimbledon -- and we were getting paid!"
Reporting by Martyn Herman; editing by John Stonestreet