July 24 (UPI) -- World No. 1 Novak Djokovic won in straight sets, as expected, while Team USA went 0-4 in singles play to open the tennis tournament at the 2020 Summer Games on Saturday at Ariake Tennis Park in Tokyo.
Djokovic beat Bolivian Hugo Dellien 6-2, 6-2 to move on to the second round. The Serbian fired seven aces, converted two of three break points and committed just nine errors in the 61-minute match.
No. 2 Daniil Medvedev of the Russian Olympic Committee and No. 11 Pablo Carreno Busta of Spain were the other top men's players to advance Saturday in Tokyo. Carreno Busta beat American Tennys Sandgren in straight sets.
Russian Aslan Karatsev also beat American Tommy Paul in straight sets.
No. 8 Iga Swiatek of Poland was the top women's player to advance. She beat Germany's Mona Barthel in straight sets. No. 11 Barbora Krejcikova of the Czech Republic, No. 12 Belinda Bencic of Sweden and No. 19 Maria Sakkari of Greece were the other top women to advance.
Krejcikova advanced due to a retirement from Kazakhstan's Zarina Diyas. Bencic defeated American Jessica Pegula in straight sets.
Sakkari beat Estonia's Anett Kontaveit in straight sets.
No. 41 Marketa Vondrousova of the Czech Republic upset No. 21 Kiki Bertens of the Netherlands in the first round of the women's tournament.
No. 168 Mihaela Buzarnescu of Romania upset No. 36 Alison Riske of the United States. Buzarnescu won that match in three sets.
Men's doubles team Frances Tiafoe and Rajeev Ram provided the only positive outcome for the Americans. They beat the Russian Olympic Committee's Karen Khachanov and Andrey Rublev in straight sets to advance to the second round of the doubles tournament.
Tiafoe and Marcos Giron are the only Team USA players who remain in the men's singles tournament. No. 15 Jennifer Brady is the only Team USA player left in the women's singles tournament.
The women's singles final is July 30. The men's singles final is July 31.