Russia's Evgeny Tishchenko won the Olympic heavyweight boxing gold medal, defeating Kazakhstan's Vassiliy Levit in a match so close that spectators booed the judges' unanimous decision.
Levit appeared to control much of the fight, but the three judges gave Tishchenko the win in a score of 29-28.
In the track cycling men's omnium, Italy's Elia Viviani looked as though he would be out of contention for a medal following a mid-race crash, but he came back to win gold, finishing in Rio's Olympic velodrome.
Monday's competition also saw more gymnastic events.
U.S. gymnast Simone Biles wobbled on the balance beam, preventing her from reaching a goal to become the first female gymnast to win five gold medals in a single Olympics. Biles took bronze in the event and goes for her fourth gold Tuesday in the floor routine. Sanne Wevers of the Netherlands took gold on the balance beam and Laurie Hernandez of the United States won silver.
In men's gymnastics, Ri Se Gwang of North Korea took gold in men's vault and Eleftherios Petrounias of Greece won gold on still rings.
In the Greco-Roman wrestling 130kg title, Mijain Lopez Nunez won Cuba's second gold medal of the 2016 Olympics as he beat Turkey's Riza Kayaalp.
Later Monday, world champion Allyson Felix goes for her fifth Olympic gold medal when she runs in the women's 400-meter final.
On Sunday, Jamaican sprinter Usain Bolt retained his status as the fastest man in the world. He won the men's 100 meters Sunday for a third-consecutive Olympics, something no runner had ever done before.
Bolt started the race slowly, but surged past American Justin Gatlin around the 80-meter mark to win with a time of 9.81.
The victory ignited cheers from a huge crowd watching the race on a screen in Jamaica's capital, Kingston. Bolt still has more he wants to accomplish at the Rio Olympics, where he is also trying to win the 200 meters and the 4x100 relay for a third time.
"Stay tuned, two more to go," he said Sunday. "Somebody said I can become immortal. Two more medals to go and I can sign off. Immortal."