The Greek says she needed a win like today's, for her confidence.
Two-time US Open champion Andre Agassi will play a different sport's US Open this weekend.
"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.
