Michael Phelps celebrates winning the men's 100m Butterfly final on Day 7 of London 2012.

Michael Phelps won the 17th Olympic gold medal of his career, and his 21st overall, when he produced a majestic performance in the 100m Butterfly.

It was the final individual race of the 27-year-old's career, which will end tomorrow night in the 4 x 100m Medley Relay.

Tonight, the Baltimore swimmer was seventh at halfway, with Milorad Cavic first, before the USA swimmer produced a customary storming final length to touch in 51.21.

Chad le Clos, who had relegated Phelps to second in the 200m Butterfly earlier this week, was second.

Earlier, teenager Missy Franklin claimed gold in the women's 200m Backstroke in a new world record time tonight.

Franklin lowered Kirsty Coventry's world mark set in 2009 by 0.75 to 2:04.06.