Rafael Nadal made another vow. To work to get back to his elite level. Again. After another loss. On clay.

The No. 5 player in the world failed to reach the finals of a minor tournament on the surface on which he never used to lose.

Rafael Nadal Starting To Slump On Favorite Surface

Nadal lost in three sets to Pablo Cuevas, the No. 45 player, 6-7 (6), 7-6 (3) 6-4, in the semifinals of the Rio Open in Rio de Janeiro over the weekend, one week after he lost in the semifinals of the Argentina Open to Dominic Thiem.

It was only the second time since 2005 that Nadal lost to a player ranked outside of the top 30 on clay, according to The Times of India.

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Nadal's deteriorating game hadn't affected his moniker as King of Clay, even after he lost in the quarterfinals of the 2015 French Open to Novak Djokovic to end a 69-1 record in the previous 10 years at Roland Garros.

Now, Nadal is sounding like a broken record of a man in search of his professional identity.

"I lost an opportunity, that's it," a dejected Nadal said, according to the Daily Mail.

"I fought until the end. I have to accept it and keep working to try to change the dynamic. That's what's happening today and I have to work hard to change it.

"I didn't win a title, so it wasn't a positive two tournaments. I had my chances in both. I lost in the semi-finals of both tournaments and just have to look forward to Indian Wells."

Nadal still is fighting to recover the confidence he lost between 2014 and 2015. He suffered a back injury during his 2014 Australian Open championship match loss to Stan Wawrinka.

That was the beginning of a list of injuries that made Nadal alter his play and fall short of the results to which he's accustomed. A bout of appendicitis at the end of 2014 prevented Nadal from preparing for 2015, and his lost confidence became more mental than physical.

Still, an "unprepared" Nadal advanced to the quarterfinals of the 2015 Australian Open.

He did not report a physical ailment in 2015, but he admitted that he had lost his confidence as the year went on.

That confidence has stayed away. Nadal lost in the first round of the 2016 Australian Open and failed to defend his 2015 Argentina Open crown.

Which begs the question of whether Nadal is really looking forward to Indian Wells like he says.

Or dreading it.

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