Novak Djokovic says he understands Rafael Nadal's confidence issues, having experienced how difficult it is to remain confident year after year. The world No. 1 has heard that the Spaniard said he is being affected by nerves, with the Serb having faced similar challenges.

“More or less every single match you go through these moments,” Djokovic said. "We are all humans and we all go through certain emotional ups and downs. Depending on the, I'd say, quality and intensity of the match, that's how your emotions kind of wave during the play.”

The two have had plenty of high-quality matches with each other. Nadal leads Djokovic 23-19 head-to-head. They played three times last year, with Djokovic beating Nadal in Miami and Madrid, but the 14-time Grand Slam champion won the biggest match, the French Open final. The two haven’t played this year.

“Of course I understand what he’s talking about because I'm playing for many years on this high level and I know how much pressure and expectations you have,” Djokovic said. “So I respect what [Nadal] has achieved in his career so far very much because I understand what it takes to be there, and what it takes achieve as much as he did. He has so much experience and so much success for only [being] 28 years."

Djokovic said he sees Nadal getting through this period. "I'm sure he wants to play for many more years," he said. "It's normal to have some periods of crisis, if you want to call it that, where you sometimes feel more doubt than confidence in important moments and you lose a couple of matches."

Similarly, Kei Nishikori admitted that he is always nervous, but said he can usually focus and calm down during a match. He faces John Isner in the quarterfinals of Miami.

For more than a year, the world No. 5 has been beating a number of top players, including Roger Federer, Stan Wawrinka, David Ferrer, and Milos Raonic.

“It’s always tough to fight with those nervous situation,” Nishikori said. “I get nervous every match, before the match especially. But I think it's good sign that you get nervous; to win the match and you feel motivation... That's the tennis, so you get sometimes get nervous. But when you get mentally strong you will be fine.”

Nadal, who was ousted by Fernando Verdasco in Miami, will no longer be in the Top 5 after this week.