Ryan Lochte held off Olympic champion Michael Phelps in a thrilling finish to win the men's 200m freestyle title at the World Championships in Shanghai.
Lochte, 26, clocked one minute, 44.44 seconds for gold, with fellow American Phelps taking silver in 1:44.79 ahead of defending champion Paul Biedermann.
French duo Jeremy Stravius and Camille Lacourt shared the men's 100m backstroke gold after a dead heat.
Britain's Liam Tancock, the defending 50m champion, was behind them in sixth.
France had never before won a male title at any swimming World Championships but Stravius and Lacourt clocked 52.76 seconds, ahead of Japan's Ryosuke Irie, who took bronze in 52.98.
"For me it was pretty much about getting to the final," Tancock said afterwards. "On the world stage, sixth place is not bad. I have got a couple of days now to rest and recover for the 50m and I am looking forward to that one."
Phelps, the Olympic champion and former world record holder, had led for the first half of 200m freestyle final but Lochte surged through from third-place to clinch a narrow victory.
"Michael and I have been battling head-to-head for almost eight years now," said Lochte. "It's been going back and forth and it's definitely been a good rivalry."
The women's 100m backstroke final was just as dramatic, with China's Zhao Jing winning in 59.05secs, beating Russia's Anastasia Zueva by just one one-hundredth of a second.
Natalie Coughlin of the United States was third, while Britain's Lizzie Simmonds finished seventh, matching her performance in the same event in Rome in 2009, when Gemma Spofforth took gold.
Spofforth failed to progress from Monday's heats after having her preparations wrecked by illness.
"I was in an outside lane so I was never going to be the centre of the action but that was a really strong swim from me," Simmonds stated. "I was so excited to be in the final, I had a great race and really enjoyed it."
Fellow Briton Michael Rock failed to reach the final of the 200m butterfly after clocking the slowest time in the semi-finals.
Rock, who had scraped through the heats in 16th place, said: "I am just disappointed I wasn't able to produce the result I wanted. I don't want to make excuses but I have been unwell with an upset stomach and have not had the best few days."
Phelps, who could still win five gold medals in Shanghai, clocked the third-fastest time behind Japan's Takeshi Matsuda and China's Chen Yin.
Rebecca Adlington and Jo Jackson were unable to get out of their heat in the women's 200m freestyle.
The four-length race is not one of Adlington's main events, but Jackson was disappointed to finish seventh in her heat and 23rd overall with a time of 1:59.40 seconds. Adlington was eighth in the same race, finishing 0.4 seconds back.
Rebecca Soni of the United States defended her women's 100m breaststroke title, finishing ahead of Australian Olympic champion Leisel Jones and China's Ji Liping who took silver and bronze.
And Denmark's Lotte Friis led from start to finish to win the women's 1,500m freestyle final, with Kate Ziegler of the US taking silver and China's Xuanxu Li earning bronze.