Venus Williams and Agnieszka Radwanska were dumped out in the first round and John Millman became the only player in Olympic history to record a double-bagel victory in a men's singles match on the opening day of the Games.
United States stalwart Williams, seeded five, was upset 4-6 6-3 7-6 (7-5) by Belgium's Kirsten Flipkens in Rio on Saturday, 16 years after winning the singles title in Sydney.
Radwanska endured a nightmare 55-hour journey to Brazil following flight woes and the Pole's persistence was not rewarded, losing 6-4 7-5 by China's Zheng Saisai. The 2012 Wimbledon runner-up broke her racket on court as fatigue appeared to catch up with her.
Millman had no reason to get wound up in the 50 minutes he spent on court, with the Australian going down in the history books by crushing Ricardas Berankis of Lithuania 6-0 6-0.
Novak Djokovic was in action in the men's doubles at the Olympic Tennis Centre, teaming up with Nenad Zimonjic to beat Croatia's Marin Cilic and Marin Draganja in straight sets for Serbia.
Japan's Kei Nishikori, seeded four, progressed to round two at the expense of Spaniard Albert Ramos-Vinolas, while Timea Bacsinszky was another seed to bow out in the women's singles when the Swiss was beaten by China's Zhang Shuai.
RALLY OF THE DAY
Nishikori dropped his racket after serving to Ramos-Vinolas, but reacted to quickly to pick it up and fire over a backhand before going on to win a point despite downing tools.
The world number six said: "I usually give up the point, but this time I saw that if I got it right back I would have the chance to win the point, so I tried to hang in there and luckily I got a point. It was the first time that it happened like that."
QUOTES OF THE DAY
"I didn't have enough time that I wanted to have here. Three days of sitting on planes, waiting at airports is not the best preparation. Another day, for sure, would have been something I could have used. I started flying on Monday morning and I got here late Wednesday night. I got a lot of airline points so I'm going to be gold [with the airline] forever." - Radwanska on her marathon trip to Rio.
"It's well documented I've had a few shoulder surgeries. To play in an Olympic Games is special. To be put in the record books is ridiculous." - Millman revels in his thrashing of Berankis.
"I'm a little tired. I'm going to bed early tonight. But it was something that I could not miss. Because I came here, that was such a special moment that I'll remember for the rest of my life. If anything it motivated me more today. But I'll sleep early." - Eugenie Bouchard reflects on attending the opening ceremony after beating Sloane Stephens in the women's singles.
World number one Serena Williams starts the defence of her singles title against Australia's Daria Gavrilova in the second game on Centre Court on Sunday.
Djokovic, the top men's player in the world, takes on Juan Martin Del Potro in a potentially tricky first round match on day two of the Games, while Andy Murray, Rafael Nadal, Garbine Muguruza and Angelique Kerber also start their bids to win singles medals.
London 2012 gold medallists the Williams sisters are in doubles action, while Wimbledon champion Murray and his brother Jamie play in the men's doubles.