Rafael Nadal is back in title-winning form…

The 27-year-old Spanish tennis star, currently ranked No. 1 in the world, won his fourth Madrid Open title on Sunday after Japan’s Kei Nishikori was forced to retire their match with an injury when trailing 2-6, 6-4, 3-0 in the men’s final.

Nishikori’s powerful groundstrokes helped him win the first set against the Nadal, who couldn’t find a way to counter his opponent.

Nadal slowly worked his way back into the match and broke Nishikori twice in the second set to even the match.

But Nishikori was in obvious discomfort in the third, even receiving treatment on his lower back during a medical timeout, before calling it quits.

Nadal recovered from two recent quarterfinal round losses on clay to win his second title on the surface this year. He began his clay court season with a quarterfinal loss to David Ferrer in the Monte Carlo Masters. He was also stunned by Nicolas Almagro in the quarterfinals of the Barcelona Open.