China's 4x200 meters freestyle relay team thought beating Canada to win bronze was a realistic target ahead of the women's final yesterday, so winning gold in a world-record time was beyond their wildest expectations.
Zhang Yufei, who won the 200m butterfly gold earlier, Yang Junxuan, Tang Muhan and Li Bingjie took an early lead and fought hard to hold it.
Li fought off a Katie Ledecky - who had the fastest leg - to keep ahead of the United States for a winning time of seven minutes, 40.33 seconds.
The US clocked 7:40.73 to win silver ahead of hot favorites Australia in 7:41.29, as all three teams finished under the Australians' previous world mark of 7:41.50.
It is the first time neither Australia nor the US have won gold since the event was introduced in 1996.
"We didn't expect to win the race because the Americans and Australians are so strong," said Zhang said. "We thought maybe we could be competitive with Canada so when we talked about tactics we just talked about what we would do against Canada."
The Chinese team gleefully hugged each other and celebrated on the podium.
"These girls swam their lights out," Ledecky said.
At a news conference later, the team shrugged off a question about how many times the four had been drug-tested over the past year. "Our drug tests have never stopped," Li said. "Chinese athletes are subject to the largest number of drug tests in the world."