|Olympics 2012 Swimming Results|
Phelps produced another majestic performance in the 100m Butterfly to touch in 51.21, winning his third London Olympics gold, the 17th Olympic gold medal of his career, and his 21st Olympic medal overall.
South African Chad le Clos, who had relegated Phelps to second in the 200m Butterfly earlier this week, tied in second place with Russian Evgeny Korotyshkin.
Most decorated Olympian Phelps is expected to finish his Olympic career Saturday with the men's 4x100m medley relay.
Missy Franklin also claimed gold in the women's 200m Backstroke in a new world record time, lowering world mark set in 2009 by 0.75 to 2:04.06. Anastasia Zueva of Russia finished second, with USA's Elizabeth Beisel third.
With the victory, the 17-year-old phenom became the first American woman in 40-years to win gold in the 200m backstroke.
With three golds and a bronze under her belt from the London Games already, Franklin is regarded as one of, if not the best female backstroker in the world right now.
Meanwhile, another member of the US swim did an impressive performance on Friday. Fifteen-year-old Katie Ledecky produced the second fastest 800m Freestyle in history to take gold for the USA.
Ledecky led from start to finish as the expected duel between world record holder Rebecca Adlington of Great Britain and Denmark's Lotte Friis failed to materialize. Spaniard Mireia Belmonte Garcia took the silver while Adlington settled for bronze.
Later on, Frenchman Florent Manaudou ended Team USA's winning streak by powering to victory in the men's 50m Freestyle. Cullen Jones of USA and Cesar Cielo of Brazil took the silver and bronze, respectively.