Serbia’s Novak Djokovic, the top-ranked men’s singles tennis player in the world, is into the quarterfinals at the Tokyo Olympics.

Djokovic defeated Spain’s Alejandro Davidovich 6-3, 6-1 in the third round at Ariake Tennis Park on Wednesday. Djokovic hit nine aces in the one-hour, 23-minute effort.

The win marked the 68th straight for the 20-time Grand Slam champion, who’s vying to become the first man to win a calendar “Golden Slam” (all four Grand Slams plus the Olympics in one year). Steffi Graf. who did it in 1988, is the only player to achieve the feat thus far.

Djokovic, a four-time Olympian, is yet to win a gold medal. He’s finished as high as third overall (2008), but did advance past the semifinals in 2012 or 2016, in both of which he was eliminated at the hands of Juan Martin del Potro.

By far the biggest name remaining across the men’s and women’s singles contests, Djokovic is also entered in the mixed doubles tournament alongside Nina Stojanovic. The pair faces Brazil’s Luisa Stefani and Marcelo Melo later on Wednesday.