Brock Whiston denied Great Britain team-mate Alice Tai a seventh gold medal at the World Para-swimming Championships with a world record victory in the SM8 200m individual medley.
Tai, who has swept all before her this week, described the medley as a "bonus event" on her schedule and was fourth.
Whiston, in her first major championship, beat American Jessica Long into second.
She took the American's world record.
There were silvers on the penultimate day of action for Ellie Robinson, Reece Dunn and Bethany Firth.
It means GB have 39 medals, including 15 golds, going into Sunday's final day of competition.
Whiston, 22, has hemiplegia, which causes weakness down one side of her body and was a talented swimmer in non-disabled competition before she realised that she was eligible for Para-swimming.
"When I was about 15 I was starting to find things difficult in training and had been suffering with a lot of dislocations in my shoulder," she told BBC Sport.
"We were at nationals a couple of years ago and one of the English Para-swimming team asked me if I had ever thought about para-swimming, which I hadn't.
"I watched Ellie Simmonds's 400m freestyle race at London 2012 and to be here following in her footsteps is just incredible."
Whiston's strength is her breaststroke and despite turning 10 seconds behind Tai into the breaststroke leg, it took her less than 25m to overhaul her team-mate and take a lead which she never looked like losing.
She finished in two minutes 35.30 seconds, beating Long's old mark, set at the US Paralympic trials in 2012 by 0.7secs.
"To have raced Jess and Alice, two of the best swimmers in this category, and come away with a gold is amazing," she added.
"I don't think it has sunk in. Jess's world record was incredible and to now hold it, I can't ask for anything more from my first major championship."
Whiston, who was also part of the victorious medley relay on Friday, goes again on Sunday in the 100m breaststroke where she is favourite for a third gold, while Tai said that she was still happy with her display.
"I know Brock has got an insanely strong breaststroke so my coach's game plan was 'Go out hard and if you die, at least die trying!' And that is exactly what happened," she said.
"Halfway down the breaststroke leg, I couldn't feel my body and when I turned onto the freestyle I thought 'oh dear'.
"But I haven't trained for the medley - I don't train breaststroke at all and fourth is a good outcome."
Paralympic champion Robinson saw her S6 50m butterfly world record of 35.22secs disappear at the hands of 14-year-old Chinese rival Yuyan Jiang who was winning her third gold of the week.
The 18-year-old from Northampton has vowed to use the defeat to spur her on for next year's Games in Tokyo.
"I'm really, really disappointed, not with coming second, but my time wasn't as close to my PB as I would want it to be," she said after finishing in 35.61secs with Jiang clocking 34.86.
"I knew it would be really difficult because the Chinese girl has done really well here but I will go away and use this as motivation.
"She's not too far front of me and hopefully I can use it to question myself more in training. Having that threat is nice but now I want to put myself in the best place for Tokyo so when we stand on the block nobody knows who will win."