JOIN USPacy Filho makes his mark in 100 free
The Brazilian swam 46.91 seconds to beat the absent Eamon Sullivan's Beijing Olympic time of 47.05. Olympic champion and favourite Alain Bernard was second with French compatriot Frederick Bousquet third.
"I think the three of us took swimming to a new level. I did it," Cielo Filho told reporters.
Bernard was the first to break the 47 second barrier at the French championships in April but his time was not ratified because his hi-tech swimsuit was not approved. The Frenchman clocked 47.12 to finish second.
Ryan Lochte smashed Michael Phelps' world record to win the men's 200 metres individual medley final. The American swam one minute 54.10 to beat Phelps' Beijing Olympic time of 1:54.23.
Hungary's Laszlo Cseh, who arrived at the championships with a stomach problem, was second with Eric Shanteau of the United States taking bronze.
The result was never really in doubt from the off with Lochte storming through the water in each of the four strokes.
Three-times champion Phelps decided not to defend his title this year after scaling back his programme.
Lochte, second to his compatriot in Melbourne in 2007, showed no mercy in stealing his crown and his record.
The 24-year-old already had one gold from Rome after the US 4x100 freestyle relay team triumphed on Sunday.
"Everytime I look up I see an American," Cseh told reporters.
In the women’s section, Australia's Jessicah Schipper broke the world record to retain her women's 200 metres butterfly title. She clocked two minutes 3.41 seconds to beat the mark of 2:04.14 set by American Mary Descenza in Wednesday's heats.
China's Olympic champion Liu Zige came second with Hungary's Katinka Hosszu taking the bronze medal.
China made a big leap on the day, winning two gold medals. Zhao Jing seized gold in the women's 50 metres backstroke final while the Chinese women also picked up the 4x200M freestyle title. Zhao stormed off the starting blocks and never relented to win in 27.06 seconds, beating the 27.38 mark Russia's Anastasia Zueva set in Wednesday's semi-finals.
Germany's former world record holder Daniela Samulski, who also lowered her own mark in the first semi before Zueva took it down further in the second, won silver. Zhao's compatriot Gao Chang claimed the bronze medal with Zueva only fourth. China destroyed the world record to capture gold in the 4x200 freestyle relay final. The quartet of Yang Yu, Zhu Qian Wei, Liu Jing and Pang Jiaying won in seven minutes 42.08 seconds, more than two seconds better than Australia's mark of 7:44.31 from Beijing.
Results: Men: 100M freestyle: Cesar Cielo Filho (Brazil) 46.91 seconds (world record) 1; Alain Bernard (France) 47.12, 2; Frederick Bousquet (France) 47.25, 3. 200M individual medley: Ryan Lochte (US) 1:54.10 (world record), 1; Laszlo Cseh (Hungary) 1:55.24, 2; Eric Shanteau (US) 1:55.36, 3. Women: 50M backstroke: Zhao Jing (China) 27.06 (world record), 1; Daniela Samulski (Germany) 27.23, 2; Gao Chang (China) 27.28, 3. 200M: Jessicah Schipper (Australia) 2:03.41 (world record), 1; Liu Zige (China) 2:03.90, 2; Katinka Hosszu (Hungary) 2:04.28, 3. 4x200M freestyle relay: China 7:42.08 (world record), 1; USA 7:42.56, 2; Britain 7:45.51, 3.