Michael Phelps on Saturday equalled Mark Spitz's record of seven gold medals at one Olympics as he took the men's 100- metre butterfly at the Beijing Games, dpa reported.
Zimbabwean Kirsty Coventry and Britain's Rebecca Adlington, both won golds in world record times and Cesar Cielo took a first-ever swimming gold medal for Brazil.
The 41-year-old Dara Torres, meanwhile, could become the oldest- ever swimming gold medallist after qualifying for Sunday's women's 50m freestyle with the fastest time.
Away from the swimming Valeriy Borchin won the men's 20 kilometres race walk gold medal for Russia and Oleksandr Petriv of Ukraine won the men's Shooting 25m Rapid Fire Pistol.
But once again it was Phelps in the Water Cube who grabbed the headlines with his most dramatic individual gold of these games.
He looked beaten at the turn when lying seventh but somehow he managed to win on the last stroke as he beat Serbian Milorad Cavic by just one hundredth of a second.
The Executive Director of the sport's governing body FINA, Cornel Marculescu, confirmed afterwards that the Serbian team had lodged an official written protest.
"This was turned down and written reasons were given to the Serbian team. We also allowed them to look at the video footage of the swim," he said.
"Although this is normally not permitted, we decided to do it to be transparent and to show that we have nothing to hide. The Serbians looked at it and were happy."
Phelps' time of 50.58 was an Olympic record. Bronze went to Australian Andrew Lauterstein in 51.12.
The 23-year-old said: "When I took the last stroke I thought I lost the race there, but it turns out that was the difference.
He added that he did not think it was automatic that he would win his eighth gold medal in the 4x100m medley relay on Sunday. "It's not over yet. I really think the Australian team looks great for the relay. It's going to be a tough race."
Coventry finally won Olympic gold in Beijing after earlier picking up silvers in the women's 100m backstroke, and the 200m and 400m individual medley.
The Zimbabwean won in a world record time of two minutes 05.24 seconds, beating previous record holder American Margaret Hoelzer by 0.99 seconds. The bronze went to Japan's Reiko Nakamura in a time of 2:07.12.
Cielo won a first-ever Olympic swimming gold medal for Brazil as he took the men's 50m freestyle in a time of 21.30.
There were tears as he came out of the water having beaten the French duo of Amaury Leveaux (21.45) and 100m freestyle winner Alain Bernard (21.49) into second and third place.
Britain's Adlington won her second gold as she smashed the oldest existing swimming world record to win the women's 800m freestyle in a time of 8 minutes 14.10 seconds.
The previous record was 8:16.22 set by American Janet Evans in 1989.
Second place went to Italian Alessia Filippi in 8:20.23, while Denmark's Lotte Friis took bronze in 8:23.03.
In the women's 50m freestyle, American swimmer Torres qualified for Sunday's final with the fastest time of 24.27, with Australian Cate Campbell and Germany's Britta Steffen having the second and third-fastest times. Torres won silver in a freestyle relay on August 10.
In Athletics, Borchin won the men's 20 kilometres race walk gold medal for Russia, holding off the three-time reigning world champion Jefferson Perez of Ecuador.
Borchin, 21, shook off Perez in the closing stages on a course in Beijing's Olympic Green to win in hot and sunny conditions in 1 hour 19 minutes 1 second.
Perez trailed by 14 seconds in 1:19:15 hours and later collapsed in the mixed zone although he recovered shortly afterwards.
The day's other three finals - men's 100m, women's shot put and heptathlon - were all scheduled for the evening.
World champion Valerie Vili of New Zealand dominated shot qualifying with 19.73, and the 2005 worlds winner Nadzeya Ostapchuk of Belarus also made it to the evening decider.
While Natalia Dobrynska of Ukraine snatched the heptathlon lead into the final javelin and 800m events with a long jump of 6.63m for a five-event total of 5,045 points.
US champ Hyleas Fountain dropped to second with 5,029 and Lyudmila Blonska of Ukraine is third with 4,913 points.
Elsewhere in qualifying there were no surprises as the sprint favourites in both men's and women's 100m came through their heats and Russian world and Olympic champion Yelena Isinbayeva required just one jump, over 4.60m, to qualify for the pole vault final.
Kenya took a first step towards another 3,000m steeplechase sweep when Ezekiel Kemboi (2004 Olympic champion and three-time runner-up at the worlds) Brimin Kiprop Kipruto (2007 world champion and 2004 Olympic silver medallist), and Richard Kipkemboi Mateelong all made the final.