"It took me as long as it took because I needed time to be convinced that the decision I was making was right," Rafa Nadal said of his retirement.
Rune is back in the Top 10 after a year outside.
Djokovic could meet his Spanish rival in the semis.
The Pole is defending champion at the Madrid Open.
The Spaniard says the tennis didn't surprise him, but the discipline did.
"I told myself, ‘OK, what did Novak do when he beat him?' " Holger Rune said.
Novak Djokovic shared some face time with Madrid's elite soccer stars.
