One of the differences between us is that he is playing in the Australian Open next week and I'm not. But as he winds up to wallop his first serve in his opening game, I know he will be thinking something like this: "Don't swing the right leg round. Hop forwards on the left." And he will be hoping his new technique will not only win him the match but spare his back from further torment. Cash's old serve - club the ball with the right arm, follow it round with the right leg and race it to the net - generated a lot of torque but only at the cost of a short spinal shelf-life. The new Cash serve was tailor-made for him in Sydney by Brad Langevad, Australia's new tennis Svengali who promises to put Nick Bollettieri and all other gurus out of a job.
My road to Damascus began on a tarmac court at Glenmore Road Junior School overlooking Sydney harbour where my four-year-old son was having his first tennis lesson. Patrick Jensen's gospel ran counter to everything I had ever learned. "I'm just one of the apostles," he said modestly, and drove me to Jensens Tennis Club in Alfred Park to introduce me to the man he called "the Messiah".
Brad Langevad is tennis's answer to Albert Einstein and Billy Graham combined. He has come up with the "Grand Unified Theory" and is marketing it in book and video form under the heading of Sports Biometrics. "This is the answer to all your problems," heassured me. "It'll even improve your surfing."
Langevad is a physiologist who was doing research on fat cells in sheep when he had the idea of applying his techniques to tennis. He started analysing body angles, then he got hooked and brought the laptop home and collected all the tennis videos he could get his hands on and built up a statistical overview.
Eureka - nothing the pros were doing corresponded with what the coaching textbook says they ought to do. Top-level practice has completely broken away from theory, but we're still teaching the old orthodoxy. "I felt as if I'd been touched by God," he said.
The great news is that he has come up with a simple solution to that old conundrum: How come we can't win Wimbledon anymore? Forget history, psychology, and the weather. The answer is footwork. We've been putting all our weight on the front-foot when al l along it should have been on the back. This is what Langevad calls "front-foot anxiety".
He worked through a tape of Newcombe-Laver and for two hours they did not play a single forehand off the front foot. "You never want to be on the front foot," he said. "Except through momentum." He is not exactly preaching lean back and scoop, but as a learning technique he encourages people to try it just to overcome the opposite tendency.
"Side-on anxiety" is Langevad's next point of attack: you should be facing the net more or less front-on, not sideways - so you can eye your adversary, not peek at him over your shoulder. Langevad said his whole philosophy could be summed up as: "get outyour tennis textbook and do precisely the opposite."
In Sydney new converts were flocking to Jensens Tennis Club. One securities trader was seduced because he agreed that "you make it by breaking all the rules". A 12-year-old boy said simply: "That was the best day of my life." The Australian Tennis Federation is rumoured to be making approaches.
Back in Fulham and equipped with the Langevad serve, Pat Cash nevertheless had a more advanced attitude towards the coach's global claims. His career might have been scripted by an author with a highly melodramatic imagination. "One minute you win Wimbledon, the next you can't walk," as he put it. He has had to make more comebacks than Sinatra. He is an intuitive player who likes to rely on raw natural talent. But his body - discs, cartilages, tendons , appendix - has kept more surgeons and physios and trainers in gainful employment than most injury-stricken football teams.
The long periods of enforced inertia, after a couple of days of wishing it had happened to Pete Sampras instead, have turned Cash into a contemplative observer of the tennis scene. He is ready and willing to apply technology to tissue. A forthcoming edition of the BBC programme How Do They Do That? shows Cash demonstrating the "dual biofeedback" device which he plugs into his knee to give an instant read-out of the relative ergs exerted by his outside and inside muscles.
However, Cash remains sceptical about the notion of a "science of tennis". He is not going to turn his game upside down. If it ain't broke, don't fix it, is his view. "I was always being told to change my backhand - and that's my best shot."
With John McEnroe, he has led a backlash against the depersonalisation of tennis. "Every player is different. Becker is the classic example. Everyone started trying his serve - with more of a forehand grip - and before long no one could serve any more - not even Becker."
Langevad's answer is that "without a purely intellectual system which tells you what is and is not truth, you're lost." He is just as much against anonymity in tennis as Cash. "With this system, you're not cloning players - you're freeing them. You have
no play with emotions - like a wild animal. My technique opens up your individuality."
Sports Biometrics will probably be seen as the zen of tennis, but technically it is more pre-Socratic, privileging the pagan instinctive way we used to play before coaches came along and started screwing us all up.
Langevad may not be doing away with idiosyncratic tennis players, but he is liable to cause a sharp rise in unemployment among the coaching profession. He offers a system of coaching which is anti-coaching. "Ultimately this is the death of coaches or coaches as we know them," he said. "The coach of the 21st century will become a manager, an organiser, or a psychologist."
According to Langevad, "guys like Bollettieri and Tiriac are just guessing - they happen to be the best guessers in the world, that's all. Bollettieri is astute, but he has got Agassi and Courier in a mess. With my system, I can tell Andre exactly what is wrong with his backhand."
Langevad is a prophet virtually without ego. "It's almost too much for me," he said, "too much responsibility. At heart all I want is to be a beach bum." But at the same time his faith is absolute: "Sports Biometrics is going to give the world the truth about sport."
Tennis is just the start of his global revolution. Already stored in the computer are golf, skiing, and, finally, anything else. "I haven't even touched running yet. But I bet the bad runners are leaning too far forwards. I bet I can even fix Michael Jordan's baseball technique. He's probably too far forwards."
Having only recently emerged from involuntary retirement, Cash doesn't realistically expect to be in world-beating form until later in the year. As for me, Langevad said: "you can be as good as you want to be."
Jensen promised: "I can make you into a pro - it isn't too late." I've got rid of the old front-foot anxiety all right. Now all I need is someone to fix my back-foot anxiety.