[1] U.S. swimmer Michael Phelps set a new Olympic record of 50.58 to defend his title in the event, edging out Serbia's Milorad Čavić (50.59) by one hundredth of a second (0.01).

[2][3][4] Australia's Andrew Lauterstein earned a bronze in 51.12, finishing in a close race against world record holder Ian Crocker by the slimmest margin.

[2] Out of five individual events from his Olympic program, Phelps did not break the current world record in a final, finishing 0.18 of a second behind Crocker's time of 50.40, set in 2005.

[5] Due to a combination of the venue, Beijing National Aquatics Center (better known as the Water Cube), which was claimed to be built to increase the speed of the swimmers,[6] and the recently introduced LZR Racer swim suits, which had been proven to give the swimmer a lower time by 1.9 to 2.2%,[7] some analysts were predicting that many fast times and world records would be set in all the swimming events.

[11] Although holding the world record, Crocker had lost the last four times that he was up against Phelps in the 100 metre butterfly, including the 2008 United States Olympic Trials.

[12] At the 2008 European Championships, Čavić won the men's 50 metre butterfly and was the heavy favorite to win at twice that distance, but was suspended for wearing a "Kosovo is Serbia" T-shirt on the medal podium.

[12] American swimmer Gary Hall Jr. told The New York Times that although "Mike (Phelps) has been saying he's going to win the 100 fly at the Olympics for the last year", he thought that Čavić would be the winner.

[15] Heats 2, 3, and 4 were won by Shaune Fraser (Cayman Islands), Rimvydas Šalčius (Lithuania), and Jakob Schioett Andkjaer (Denmark), respectively.

[5] South African Lyndon Ferns was the first swimmer to qualify for the semifinals, winning heat 5 with a time of 52.04 seconds,[15] while national records were broken by Mario Todorović (Croatia), Simão Morgado (Portugal), and Douglas Lennox-Silva (Puerto Rico).

[15] Five of the eight swimmers in heat 7 advanced as well, including Jason Dunford (Kenya), Andrew Lauterstein (Australia), Takuro Fujii (Japan), Frédérick Bousquet (France), and Ryan Pini (Papua New Guinea).

[15] The swimmers qualifying from heat 8 were Albert Subirats Altes (Venezuela), Corney Swanepoel (New Zealand), and Ian Crocker (United States).

[15] Heat 9 was the fastest one, with Milorad Čavić (Serbia), Michael Phelps (United States), Andrii Serdinov (Ukraine), Peter Mankoč (Slovenia), and Kaio de Almeida (Brazil) all earning spots in the next round.

[15] Surprisingly, Albert Subirats Altes, the bronze medalist at the 2007 World Championships,[9] failed to qualify, after finishing in the sixth place.

[4] For being able to emulate Spitz's record, Speedo, a sponsor of Michael Phelps, awarded him a US$1 million bonus, which had already been offered to him at the 2004 Summer Olympics, under the same conditions.

"[4] Almost immediately after the end of the race, the Serbian team filed a protest claiming that Čavić touched the wall first but did not use enough force to trigger the timing sensor.

[20] Officials of the International Swimming Federation (FINA) watched the video in slow motion, and announced that Phelps' victory would be upheld.