RIO DE JANEIRO - Even in defeat, swimming legend Michael Phelps had to make history in his last individual race at the Olympics.

The most decorated Olympian of all-time added a unique silver to his haul of 27 medals.

The American clocked 51.14 seconds to finish behind Singapore's Joseph Schooling in the 100m butterfly, only to realise that South African Chad le Clos and Hungary's Laszlo Cseh also tied for second.

Schooling, 21, touched home in a Games record time of 50.39sec to win Singapore's first Olympic gold.

Before Friday, there had never been a three-way tie for any swimming medal in the history of the Olympics. But medals have been shared by two competitors.

"I don't know if I've been in a tie so a three-way touch is pretty wild," said Phelps, a 22-time Olympic champion. "I saw a second next to my name then I looked up again and I looked at Laszlo and Chad and I went we all tied for second, that's kind of cool."

In this event at the 2012 London Games, le Clos and Russian Yevgeny Korotyshkin both claimed silver in 51.44sec behind Phelps (51.21sec).

"I (tied for silver) in London so a three-way tie is crazy," said le Clos. "Maybe in Tokyo (2020 Games) there will be a four-way tie."

The 24-year-old and Korotyshkin were not the only ones to have matching efforts in the British capital. China's Sun Yang and South Korean Park Tae Hwan posted 1:44.93 to finish behind champion Yannick Agnel of France (1:43.14) in the 200m freestyle.

On Thursday, Canada's Penny Oleksiak and American Simone Manuel finished the 100m freestyle in an Olympic-record 52.70sec.

They were just the second pair of women to share gold in the blue riband sprint at the Olympics. Americans Nancy Hogshead and Carrie Steinseifer both clocked 55.92sec to stand together at the top step of the podium during the 1984 Los Angeles Games.

The last dead-heat for Olympic gold in swimming was at the 2000 Sydney Games when Americans Gary Hall Jr and Anthony Ervin both completed the 50m free in 21.98sec.