American swimming legend Michael Phelps extended his record Olympic gold medal haul to 17 with a third consecutive victory in the Olympic 100m butterfly final on Friday.

Just a day after becoming the first male swimmer to win the same individual event at three Olympics with victory in the 200m medley, he did it again.

The 27-year-old produced a strong finish to clock 51.21 seconds and finish ahead of South African Chad le Clos and Russian Evgeny Korotyshkin, who dead heated for the silver medal in 51.44.

Phelps, who earlier this week officially became the most decorated Olympian of all time, has now extended his total medal haul to 21.

He will get a chance to add another, and bow out of the Olympics with one last medal, in Saturday night's 4x100m medley relay.

After a slow start, Phelps has now won three gold and two silvers in six races in London.

While Ryan Lochte was expected to challenge as the world's premier swimmer at these Games, Phelps has ensured he will bow out firmly in the spotlight.

NZ Newswire