Japan's Naomi Osaka cruised into the third round of the Tokyo Olympics women's singles with a 65-minute victory over Viktorija Golubic.
Second seed Osaka, the favourite for the gold medal following world number one Ashleigh Barty's first-round exit, beat the Swiss 6-3 6-2.
Osaka will face Marketa Vondrousova, who beat Mihaela Buzarnescu 6-1 6-2, for a quarter-final spot.
World number one Novak Djokovic beat Germany's Jan-Lennard Struff 6-4 6-3.
Djokovic is bidding for a first Olympic gold medal after winning bronze in Beijing 2008.
Great Britain's Jamie Murray and Neal Skupski were knocked out of the men's doubles in the second round, losing 6-3 6-4 to Japan's Kei Nishikori and Ben McLachlan.