Expensive Swiss mechanical watches don't have much practical use on the field, court, or track, though it's not uncommon to see the world's biggest athletes wearing high-end, luxury timepieces during their events.

Rafael Nadal won his 19th Grand Slam title at the US Open on September 8, putting him right behind Roger Federer 's record 20 Grand Slam titles. That kind of athletic prowess is a marketing tool. Watch brands are eager to sponsor elite athletes, from tennis champions like Nadal and Federer to fighters like Floyd Mayweather , not for their horological expertise but for their aura which sells.

Read more : Rafael Nadal and Odell Beckham Jr. may play in their stupidly expensive watches, but that doesn't mean you should too

When Nadal won his latest Grand Slam title, he was wearing his famed Richard Mille timepiece, which retails for roughly $725,000 .

We got a helping hand from the experts at Crown & Caliber to determine the makes and models of 21 timepieces worn by the world's top athletes. They are listed here in ascending order of price.

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