- Michael Phelps won a record 19th gold medal as the United States secured victory in the men's 4x100 metre relay.
- World number one Novak Djokovic suffered a shock elimination in the first round of the men's singles tennis tournament, going down in straight-sets to Juan Martin Del Potro.
- Netherlands' Annemiek van Vleuten had a horror crash in the women's road race, suffering fractures in her spine as compatriot Anna van der Breggen took gold.
- Three world records were beaten in the pool, including Adam Peaty in the men's 100m breaststroke final and Katie Ledecky in the women's 400m freestyle final.
- The Williams sisters, Serena and Venus, fell victim to the Czech pairing of Barbora Strycova and Lucie Safarova in the women's doubles, the former losing their perfect Olympic record in the process.
- The Murray brothers, Andy and Jamie, were also ousted in the men's doubles, going down to Brazilian pair Thomaz Bellucci and Andrea Sa in straight sets.
QUOTES OF THE DAY
"This morning I swam, and this afternoon I play Yahtzee with my roommate. I just chilled and took it easy," said Sweden's Sarah Sjostrom, after breaking her own world record in the women's 100m butterfly final.
"He's a great champion, a friend for a long time. I know how important this event was for him. He wanted the gold medal, but I also believe he knows about my effort. I talked to him all through my rehab. I'll always be thankful for his words. We respect each other so much. It was a spectacular match from any point of view," Argentina's Del Potro said of Djokovic, following his 7-6 (7-4) 7-6 (7-2) win over the Serbian.
"I am now in the hospital with some injuries and fractures, but will be fine. Most of all [I am] super disappointed after [the] best race of my career," said Van Vleuten following her horrific crash.
PHELPS - THE MOST DECORATED
Phelps, the most decorated Olympian of all-time, added to his record tally with a 19th gold medal. The 31-year-old secured it in the men's 4x100m relay, alongside Nathan Adrian, Caeleb Dressel and Ryan Held.
Majlinda Kelmendi made history for Kosovo, winning a gold medal in the women's 52kg judo category - the nation's first ever medal at the Olympics.
Meanwhile, Peaty's world-record effort helped Great Britain register their first gold of the Games.
COMING UP: More medals up for grabs in the pool, women's rugby sevens final
Monday's action sees finals in the men's 200m freestyle, the women's 100m backstroke, the men's 100m backstroke, and the women's 100m breaststroke.
Tom Daley begins his challenge for gold as he teams up with Dan Goodfellow in the 10m synchro diving competition.
Meanwhile, the winner of the women's rugby sevens tournament will be decided, with New Zealand, Great Britain, Australia and Canada all in contention.
Brazil's football side, who boast Barcelona superstar Neymar, were held to their second scoreless draw of the men's tournament, leaving the hosts on the brink of elimination. They face Denmark on Wednesday, needing a win to guarantee a spot in the quarter-finals.