Australian Alexandria Perkins has nabbed a bronze medal, Canadian superstar Summer McIntosh continued her winning ways and the virus-stricken US finally broke their gold medal duck on day two of the swimming world championships.
Perkins produced a strong finish to snare third place in a hotly-contested women's 100m butterfly final in Singapore on Monday night.
World record holder Gretchen Walsh started the race as the hottest of favourites, but the big question was whether she had escaped the gastro carnage that has swept through the US camp.
The widespread sickness resulted in the powerful US team ending the opening night without a gold medal, with Australia beating them in both the men's and women's 4x100m freestyle relays.
Walsh put any sickness doubts to rest on Monday night with a powerful 54.73-second swim that gave the 22-year-old a maiden world championship title and brought the US its first gold of the meet.
The American now owns the eight fastest times in the 100m butterfly, with her latest effort the second best of all time.
Belgium's Roos Vanotterdijk (55.84) finished second, while Perkins came home fast to nab bronze in a time of 56.33.
"I can't be happier with that," an elated Perkins told Channel 9.
"It was a new experience being in this final tonight.
"I missed out last year at the Olympics, so I'm just really proud of myself for handling my nerves against someone like Gretchen.
"She's just incredible. She did a phenomenal job."
In what served as an entree to Tuesday night's final, Australian Olympic champion Kaylee McKeown finished second to American arch rival Regan Smith in the women's 100m backstroke semi-final.
McIntosh, who is aiming for five individual gold medals at this championships, made it two from two on Monday night.
The 18-year-old Canadian won the 400m women's freestyle on Sunday, and backed it up with victory in the 200m individual medley on Monday night.
McIntosh won the medley in a time of 2:06.69, fending off a challenge from Alex Walsh (2:08.58) in which they were almost even heading into the last 50m.
In the men's 200m freestyle, Australian Flynn Southam finished last in his semi-final heat to miss the final.
China's Qin Halyang won his fourth world championships gold medal after coming from behind to defeat Italian Nicolo Martinenghi in the men's 100m breaststroke final.
Frenchman Maxime Grousset (22.48) edged Switzerland's Noe Ponti (22.51) in a hotly-contested 50m men's butterfly final.
Australia's 16-year-old rising star Sienna Toohey swam a time of 1:07.24 in the 100m breaststroke heats but missed out on a semi-final berth by 0.24 of a second.
Toohey was in the same heat as triple Olympian and triple world record holder Lily King, who scraped into the semis with a time of 1:06.93.
"That was the fastest heat swim I have ever done," Toohey said.
"I knew I was racing Lily King but I was trying to pretend it wasn't her because I didn't want to get freaked out. But it was pretty cool."
