There were 14 gold medals to be won Sunday, with athletes from 22 sports competing.
The women's gymnastic events begin, and the Kosovo team -- appearing for the first time at the Olympics -- is represented by 2016 European champion Majlinda Kelmendi
, who is a medal prospect in the judo competition.
Here are five highlights from the second day of Brazil's sporting festival.
Might we get the first glimpse of Michael Phelps, the most successful Olympian to date? He will be looking to add to his haul of 22 medals, 18 of them gold, in this his fifth Olympic Games
. There's a chance that he might be selected to swim in the 4x100 meters freestyle relay.
U.S. teenage star Katie Ledecky
also raced Sunday, taking the gold in the 400-meter freestyle and setting a new world record in the process.
The swimmer amazed the world at the London 2012 Olympics by recording the second fastest 800m time in history and winning the gold as a 15-year-old. She has set 11 world records.
There were three gold medals to be decided Sunday -- in the women's 100m butterfly, men's 100m breaststroke and women's 400m freestyle -- but it's a very busy day in the pool with heats in many of the disciplines for both men and women.
World champion and current 100m world record holder Adam Peaty of Great Britain will face a challenge from Americans Cody Miller and Kevin Cordes, and from South African Cameron van der Burgh.
The home crowd will also be able to cheer on one of their stars -- Joao Gomes, who qualified for the event with a competitive time.
South Korea's Kim Woojin managed to set a new world record even before the opening ceremony
. The two-time world champion scored 700 with 72 arrows in the men's individual ranking round at Sambodromo on Friday.
Since archery was reintroduced into the Olympic Games in 1972, South Korea has won more than half of the available gold medals.
Sunday is the turn of the women, who take part in the team event.
London 2012 individual champion Ki Bo-Bae returns to lead South Korea's women's team, which is also seeking to defend its title.
China's Wu Minxia, the first woman to win diving gold in three consecutive Olympics, will try to break her own record and make it four in the synchronized 3m springboard event.
She is one of the most successful divers in history, having won eight world titles on top of her Olympic successes.
After the men's grueling cycle road race on Saturday
, it's the women's turn to show what they can do on the bikes.
Britain's Lizzie Armitstead, who is the current world champion, won silver at London 2012 and will start as one of the favorites to take gold on the 137-kilometer (85 mile) course.
Armitstead's appearance at the Rio Games was thrown into doubt after she missed three drugs tests -- but won her appeal and escaped a ban.
The British rider's main rival, London 2012 champion Marianne Vos of the Netherlands, will once again be a good tip for a podium position.
Feast of sport
Ever tried fencing or trampoline gymnastics? Once every four years, some of those sports that don't enjoy so much media coverage get a chance to showcase the grace and skill of the competitors -- and perhaps inspire you to have a try yourself.
The canoe slalom starts Sunday in the Whitewater Stadium and the men's foil competition will be fought out in the Carioca arena. There are medals to be won in the judo events, and the table tennis matches continue in Riocentro.
With such a festival of endeavor on display, there will surely be something to thrill and excite as the Rio Games gets into full swing.