Budapest - Katie Ledecky swept two golds on Sunday's opening day of the world championships, Sarah Sjostrom broke the 100m freestyle world record while Sun Yang gained revenge over Mack Horton in the 400m freestyle.
Ledecky, 20, began her account in Budapest by becoming the first woman to win a third straight 400m freestyle gold at the world championships.
Setting a new championship record, she also equalled Missy Franklin's record of 11 golds at world meets for good measure.
Her American compatriot Leah Smith finished 3.20 secs back, with China's Li Bingjie, 15, picking up her first world medal in third.
Later Ledecky earned her second gold of the night by helping the United States win the women's 4x100m freestyle final.
The USA pipped Australia to the win, with the Netherlands taking bronze.
"It was a good first night for Team USA," said Ledecky. "I am happy with the two wins and how it all went."
The men's team also picked up gold in the men's 4x100m freestyle as the USA won both of the relays.
The only world record to fall on day one was claimed by Sweden's Sjostrom who clocked a world record of 51.71secs for her first leg of the women's relay final.
Although Sweden were only able to finish fifth behind Ledecky's United States, Sjostrom became the first ever woman to swim under 52 seconds.
"I went all out for the first 50, and hoped for the best on the last 50," said the Swede.
"It's also much easier to go for records in the first leg of the relay, so I kind of took the chance."
Her performance now makes her the favourite for gold in the 100m freestyle final on Friday, while she is also the fastest into Monday's 100m butterfly final from Sunday's semis.
The Swedish sprint ace could also take gold in the 50m butterfly and the 50m freestyle later in the week.
Chinese superstar Sun Yang avenged a second-place finish behind Mack Horton in Rio by thrashing the Australian Olympic champion in a hotly anticipated 400m freestyle grudge race.
Horton had dubbed his rival a dope cheat prior to winning gold in Rio last year, after the Chinese served a three-month ban in 2014 after testing positive for a stimulant.
It was a "rivalry between clean athletes and those who tested positive" he said in the run-up to Sunday's race, but finished 2.47 seconds behind Sun who splashed the water and gave a triumphant roar after touching the wall.
"A long time has passed since Rio, we both got stressed, we both calmed down," Sun said.
It was "still too early to say" the Chinese superstar added when asked if he expected three more world golds to follow in Budapest with the 200m, 800m and 1500m freestyle races still to come.
"The time stings more than losing," said a