Former world No. 1 Ana Ivanovic exited the Olympic Games in the first round on Saturday, though the Serb refused to blame the wind or soaring temperatures that some players said were making it tricky to play in Rio.
Ivanovic went one set up against world No. 12 Carla Suarez Navarro before losing the next two error-strewn sets to the Spaniard. Ivanovic lost 2-6, 6-1, 6-2.
"It was a tough draw for the first round," said Ivanovic, the former French Open winner currently ranked as world No. 26.
"I had a chance to come back in the third set but every time I came close to pegging her back, I missed the opportunity," she added.
Former Olympic champion Venus Williams was eliminated in the first round after Belgian underdog Kirsten Flipkens mounted a spirited fight back to cause the biggest upset of the opening day.
With U.S. Secretary of State John Kerry and gymnastics gold medal favorite Simone Biles looking on, seven-times grand slam winner Williams won the first set but became frustrated as the match wore on, losing 4-6, 6-3, 7-6(5) to the world number 62.
The loss will not be the end of the competition for 2000 Sydney Games champion Williams, however, as the 36-year-old is bidding to win her fourth doubles gold medal with sister Serena.
Fourth seeded Agnieszka Radwanska was also a high-profile casualty, slumping to a 6-4, 7-5 loss against China's world number 63 Zheng Saisai.
The Pole only arrived in Rio on Wednesday night after having to fly from Montreal, where she competed last week, to New York to Lisbon and then to Rio. In all, she was on the move for 55 hours and covered around 14,000 kilometres.
But the size of crowds didn't bother Japan's Kei Nishikori, who opened the men's singles tennis tournament on center court by knocking out Spain's Albert Ramos-Viñolas with ease, winning 6-2, 6-4.
One person who thrived in the Rio sun was Australia's John Millman, becoming the first Olympian ever to win a men's singles match without losing a game.
Millman's "double-bagel" 6-0, 6-0, victory against Lithuania's Ricardas Berankis came after several shoulder surgeries that threatened his career. The Australian also took part in the late-night opening ceremony, which many other Olympians competing early on Saturday skipped.
"I couldn't miss the (parade). That was a really stirring moment for me. It's hard to explain the emotions I got walking into that stadium, and obviously that carried over to today," said Millman, 27, who plays Nishikori next.
"I was pumped up from the word go."