Nadal is the only player whose clay-court UTR is over 16.0. (AP) 

Rafael Nadal's 21-match clay winning streak came to an end in the Madrid quarterfinals, but he's still the King of Clay, especially with his 16.41 clay-court UTR.

A Universal Tennis Rating, or UTR Powered by Oracle, is a number from 1 to 16.5 that rates the level of any tennis player in the world of all ages, nationalities, leagues and genders. 

"It is a single rating for everyone from [Roger] Federer and Nadal and Serena [Williams] to a beginner that's starting out," said UTR's chief tennis officer, Stephen Amritraj. 

Nadal nearly broke that 1-to-16.5 scale on May 7, when his three-month trending rating reached 16.49. 

"What that means is he's pretty much been perfect over the last three months," Amritraj said of Nadal's run.

Unlike the ATP and WTA rankings, UTR considers margin of victory. At the time of his 16.49, Nadal had won all 26 recent sets he'd played, only once letting an opponent win more than four games in a set. 

 

Contento de nuevo de estar en semifinales en #monaco #vamos #semis #happy #merci

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His three-month UTR took a slight hit after his loss to Dominic Thiem, dropping down to 16.42, but that's still easily the highest on tour—Federer is in second place with 16.19.

UTR also tracks clay-specific ratings, which account for clay results over the past 12 months. For those, Nadal blows the field away with 16.41. The rest of the men's Top 5 on dirt includes Alexander Zverev (15.97), Novak Djokovic (15.88), Thiem (15.83) and Marin Cilic (15.81). 

Thiem performs notably better on clay than on the other surfaces, evidenced by him having the fourth-best clay rating and only the 12th-best rating overall (15.76). Zverev, last week's Madrid champion, is scored second on clay and fourth in general (15.90). 

Prague and Madrid winner Petra Kvitova leads the WTA in clay UTR with 13.27, followed by Karolina Pliskova (13.24), Simona Halep (13.23) and Elina Svitolina (13.22).

This sheds light on the misconception that Kvitova is only good on fast surfaces, an easy trap to fall into given her powerful play and two Wimbledon titles.

 

Feeling grateful ???????????? #23

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Two clay over-performers tied with Svitolina for fourth are Marketa Vondrousova and Kiki Bertens, ranked No. 67 and No. 15 on the WTA. 

Australian Open champion and world No. 2 Caroline Wozniacki has the tour's highest overall UTR with 13.32, but, at 13.17, is rated only the eighth-best on clay. 

 

Positive vibes today at practice???? #clay #iloveclay #mccc

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