Tennis at the Olympics began with 15 women's singles and seven doubles matches. Among the seeded singles winners were sixth seed Iga Swiatek, eighth seed Barbora Krejcikova, ninth seed Belinda Bencic, 13th seed Anastasia Pavlyuchenkova, 14th seed Maria Sakkari and 15th seed Elena Rybakina. 16th seed Kiki Bertens was upset by Marketa Vondrousova.
Top seeds victorious on opening day of action
Swiatek needed just 67 minutes to dismiss Mona Barthel 6-2, 6-2. The Pole hit 13 winners and broke the German six times en route to the second round.
"It was a special moment for me", she said following the win. "I know that right now I really feel the Olympic vibe."
Krejcikova advanced when Zarina Diyas retired after just seven games with the reigning Roland Garros champion leading 5-2. The Czech has now won 21 of her last 22 matches.
Bencic played a solid match against Jessica Pegula, coming out on top 6-3, 6-3 after an hour and 19 minutes. The Swiss won 82 percent of her first serve points and was never broken.
Pavlyuchenkova crushed Sara Errani 6-0, 6-1 in one hour, ten minutes. The Russian, runner-up to Krejcikova in Paris, broke the Italian's serve on seven occasions.
Sakkari came out on top in what looked to be the most evenly-matched first-round contest as the Greek eliminated 28th-ranked Anett Kontaveit 7-5, 6-2, to clinch a spot in the second round.
Kontaveit had a 5-2 lead in the match before Sakkari went on a five-game winning streak to steal the opening set, closing out the first and final games of that run with aces.
Rybakina also clinched a straight-set victory on opening day as she defeated former US Open champion Samantha Stosur of Australia 6-4, 6-2 in a match that lasted 70 minutes.
Other results
These matches were all between unseeded players: Anna-Lena Friedsam defeated Heather Watson 7-6 (5), 6-3, Leylah Fernandez knocked off Dayana Yastremska 6-3, 3-6, 6-0, Rebecca Peterson edged Mayar Sherif 7-5, 7-6 (1), Paula Badosa overcame Kristina Mladenovic 6-7 (4), 6-3, 6-0, Mihaela Buzarnescu outlasted Alison Riske 6-7 (0), 7-5, 6-4 and Viktorija Golubic routed Maria Camila Osorio Serrano 6-4, 6-1.
Japanese fortunes were mixed as Misaki Doi beat Renata Zarazua 6-3, 6-2, but Nao Hibino fell to Nina Stojanovic 6-3, 6-3.
Doubles results
The only seeded doubles team to advance was sixth seeds Ashleigh Barty and Storm Sanders and they had no problems with the Japanese duo of Hibino and Makoto Ninomiya, winning 6-1, 6-2. Fifth seeds Hao-ching Chan and Latisha Chan were upset by Monica Niculescu and Ioana Raluca Olaru 7-5, 1-6, [10-6] as were seventh seeds Gabriela Dabrowski and Sharon Fichman 7-6 (3), 6-4 losers to the Brazilian team of Laura Pigossi and Luisa Stefani.
Elsewhere, Xifan Yu and Zhaoxuan Yang claimed an epic 4-6, 6-4, [18-16] victory over Aleksandra Krunic and Stojanovic, Veronika Kudermetova and Elena Vesnina defeated Friedsam and Laura Siegemund 6-2, 7-5, Alize Cornet and Fiona Ferro cruised past Elina Svitolina and Yastremska 6-2, 6-4 and Garbine Muguruza and Carla Suarez Navarro upset Elise Mertens and Alison Van Uytvanck 6-3, 7-6 (4).