Rio Olympic Games medal-winners on Day 4 : 21st gold for Phelps; Serena's shock exit

In the Men's 200m Butterfly event, Michael Phelps won the gold with a timing of 1:53.36 in what turned out to be a thrilling race to the finish line between the American and Japan's Masato Sakai, who finished with a time of 1:53.40. Hungary's Tamas Kenderesi, who dominated in the heats, won the bronze.

Just an hour later, the 31-year-old was back in the pool, this time, to anchor the men's 4 x 200m Freestyle relay race. The USA team, which consisted of Conor Dwyer, Townley Haas, Ryan Lochte, and Phelps, dominated the race and finished three seconds ahead of Great Britain with a timing of 7:00.66—just two seconds behind the world record.

In weightlifting, China's Deng Wei won gold in the women's 63 kg category and decimated the world record in the process. The 23-year-old lifted 147 kg in the clean and jerk and 115 in the snatch to create  a new world record total of 262 kg in two lifts.

In tennis, World No.1 Serena Williams faced a shock exit in the third round. Ukraine's Elina Svitolina won the match 6-4, 6-3 to open up the race for the gold in the women's singles event. In another surprise result, French Open champion Garbine Muguruza lost to Puerto Rico's Monica Puig in a one-sided encounter 6-1, 6-1.

In men's singles, Rafael Nadal defeated Andreas Seppi 6-3, 6-3 in his second-round clash, while Andy Murray also cruised through to the next round with a 6-3, 6-1 win over the Argentine Juan Monaco.