Watch Rio 2016 Olympics Day Four Highlights as Michael Phelps Wins Double Gold

United States swimmer Michael Phelps.
Michael Phelps of the United States at the Olympic Aquatics Stadium, Rio de Janeiro, August 9. Phelps won two golds to take his career tally to 21. Christophe Simon/AFP/Getty

It was the Michael Phelps show on Day Four of the Rio de Janeiro Olympics.

Perhaps the greatest Olympian of all time won the 20th and 21st gold medals of his career in the 200 meters butterfly and 4x200 meters relay.

Simone Biles and the United States women's gymnastics team put in a dominant performance in the team all-around final to claim gold ahead of Russia and China. Great Britain was in the medal hunt but eventually finished fifth.

There was a shock in the tennis, as Serena Williams went out to Ukraine's Elina Svitolina in the women's singles. Williams took the gold at London 2012 but lost 6-4 6-3 to Svitolina in 72 minutes in Rio.

There was controversy in the diving pool, though it was nothing to do with the competitors, as the water turned a dark shade of green. Great Britain's Tonia Couch and Lois Toulson fought with Canada for bronze right up until the final dive of the women's 10-meter synchronized competition, before finishing fifth, while China took gold and Malaysia silver.