Graphic: The anatomy of a champion

A schoolboy error came close to costing the phenomenon that is Michael Phelps a fortune yesterday as his goggles filled with water and left him effectively to swim blind to win his fourth gold medal at the Beijing Olympic Games.

The United States swimmer is on course for the so-called "great eight" at the Water Cube, but failure in the 200 metres butterfly could have cost him the $1 million (about £530,000) bonus pledged to him by Speedo if his gold-medal haul tallies with the seven won by Mark Spitz, a compatriot, in 1972.

Phelps, who still set a world record, finishing in 1min 52.03sec, blamed no one but himself for an error seen at the local pool on a daily basis but rarely, if ever, in an Olympic final. Tackled by The Times yesterday, Phelps said: “I don't know what happened. It just kept getting worse and worse through the race and I was having trouble seeing the walls. I wanted to go 1:51 or better, but for the circumstances I guess it's not too bad.”

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Rest assured that Phelps, whose earning power could be stratospheric if he overtakes Spitz's tally, will not let it happen again. It could have been the angle of his dive, it could have been that he placed the strap too low on the back of his head or that the tension of the elastic was not strong enough to suck the goggles into the pits of his eyes. However, whereas many athletes take at least two pairs of goggles to the ready-room, where swimmers have to gather and register before walking out to race, Phelps admitted that he had taken only one. “Just the one. Always just the one,” he said.

After the race Phelps threw away his goggles and armed himself with a fresh pair for the 4x200 metres freestyle relay, which brought a fifth gold at this Games, a fifth world record and an eleventh career gold that put more daylight between the record nine achieved by Paavo Nurmi, Carl Lewis, Spitz and Larissa Latynina.

Phelps, 23, earns about $5 million a year, nearly all of it in endorsements. When he won seven gold medals and set five world records at the World Championships last year, he earned only about $200,000 in prize-money. His supreme achievement also drew comparison with Tiger Woods, the world's No 1 golfer, and Roger Federer, then the world's dominant tennis player, while back home his name was raised in the same sentences as Hideki Matsui, of the New York Yankees baseball team (who earns $19 million a year), and Dirk Nowitzki, of the Dallas Mavericks basketball team ($18 million a year).

But while his earnings are dwarfed in comparison, things are about to change and those compiling the Sports Illustrated list of the top 20 sports earners are laying out towels and mops in readiness for the arrival of the first fish on the sporting money-go-round.

Assessing his earning potential will not be easy. There are no wages in swimming, prize-money is growing but is in its infancy relative to professional sports, and appearance money is insignificant. But Phelps's income will grow the moment he matches Spitz's record. That could be on Saturday or Sunday, depending on the outcome of the 100 metres butterfly.

Speedo, the British suit-maker behind the LZR Racer, in which more than 50 world records have been set this year, is watching with a nervous smile. Four years ago it offered the $1 million bonus to Phelps if he could match Spitz's tally. He fell one gold shy and insurers celebrated. Speedo extended the deal to Beijing, but insurers refused to do a deal. Thank the aquatic gods, then, for the publicity generated by the LZR and sales that make Speedo accountants salivate.

Business, the whisper goes, is strong in Asia. Phelps is already well-established in what Ian Thorpe - who earned an estimated A$10million (£4.6 million) a year at his peak - helped to make a strong market for swimming. Phelps is well-advised by Octagon and his official website can be read in the two languages that matter most: English and Chinese.

He endorses Visa, Omega, Speedo and Matsunichi and advertises a telecommunications company and a mortgage broker at a time of the credit crunch, when every super-hero must do his bit. The deal with Matsunichi, which makes MP3 players and other electronic devices, is significant. It is worth more than $1 million a year.

Octagon is making no predictions for its client, but a four-fold increase in Phelps's earning power is said by one analyst to be “within easy reach”. That would put the swimmer among the top ten earners in sport. “He transcends swimming,” a marketing source said. “He's the greatest Olympian that ever lived. That's a very big cheque for the rest of his life, most likely.”

With Woods out of action for the rest of this year, recovering from a knee operation, and with Federer having lost his aura of invincibility, Phelps, it is widely thought here, is the most dominant athlete in world sport. His rivals are caught in the headlights. Laszlo Cseh, of Hungary, who won silver behind Phelps in the 400 metres individual medley and 200 metres butterfly, said: “Any time you think you are close to reaching him, he jumps to another level.”

Phelps's ambition beyond the pool is to “raise the status of the sport of swimming in the public's mind. I want it to be seen as a major sport.”

That will surely be a herculean task beyond anything that swimming's superhero has faced at the Water Cube this week.

Out of his depth

Michael Phelps is arguably beyond any other athlete in terms of versatility and dominance, but where money talks the “Baltimore Bullet” is floundering compared with other big names

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