Tennis great Rafael Nadal is one of the most obsessive, ritual-oriented players on the tour. From the placement of his two water bottles, to tying his shoes and wiping off the sweat from his face (always nose first, left ear, nose again then right ear), he is a man who relies on routine to win.
So when a little-known watchmaker asked if Nadal might consider wearing a watch during his matches, the answer was simple.
"I said no way," said Carlos Costa, Nadal's manager. "I know Rafa, and ... he's complicated."
In the year that followed, however, Nadal and the watchmaker Richard Mille worked together to create a superlight, hyper-engineered watch that Nadal could wear during his matches. In the process, they've also forged one of the most successful athlete-sponsor relationships in sports.
After selling out of the first Nadal watch, priced at $525,000 and launched in 2010, Mille and Nadal this year launched a second watch. It's called the RM027-01. The price: a whopping $690,000.
Mille doesn't disclose sales, but said "interest has been very strong" from its clients. As for Nadal, he not only wears the $690,000 watch during every match but says he can't imagine playing without it.
(Read more: The $500,000 Nadal watch is now sold out)
"I don't feel the watch," he said, strapping it on before practice at the U.S. Open on Tuesday. "It's very light and when I don't wear the watch, I feel like something is not working."
Of course, plenty of tennis stars have watch endorsements. Roger Federer has a deal with Rolex. Maria Sharapova helps sell TAG Heuer. But neither wear their watches on the court.