Michael Phelps wins gold in his last individual race of the 2012 London Olympics, the 100 meter butterfly, and 3-peats again in these Summer Games, winning gold over the last 3 Olympics in the same event. Phelps had a slow takeoff the block, and slow turn - he was in 7th place after 50m, but he pulled ahead and touched the wall in the short 2 laps race, at 51.21, ahead of South Africa's Chad Le Clos and Russia's Evgeny Korotyshkin, who tied for the silver at 51:44. It is Michael Phelps's 21st Olympic medal, and 16th Olympic gold in his swimming career.
The other 3-peat for Phelps was in the 200im the day before:
http://www.gymchat.com/messageboards/swimming-discussion/205212-michael-phelps-3-peats-gold-200im-2012-london-olympics-win-over-ryan-lochte.html
Phelps final race this Olympics - and according to him his Olypics career as he plans to retire after these Summer Games - is the 100m medley relay that he will be swimming with his U.S. team.