Sarah Sjostrom, who has been winning world titles for 13 years, and Summer McIntosh, who has been winning them for four days, both collected their second gold medals of the week in Budapest on Saturday.
Ms. Sjostrom, a 28-year-old Swede who won the 50m butterfly less than 24 hours earlier, added the 50m freestyle, her 10th world gold.
Ms. McIntosh, a Canadian 15-year-old, held off 16-year-old American Katie Grimes to win the women's 400m medley title.
Ms. McIntosh, who won the 200m butterfly gold on Wednesday, claimed her fourth medal in Budapest in four minutes and 32.04 seconds.
Grimes was 0.63sec back, while another American, Emma Weyant, was a distant third ahead of Hungarian 33-year-old Katinka Hosszu, the defending champion.
"I tried to push my body as much as possible," said McIntosh. "The crowd gave me so much adrenaline.
"I really felt my body in the backstroke.
"Katie is a top competitor, I like racing against her since we are in the same age group."
Ms. Sjostrom finished her sprint in 23.98 seconds, 0.20sec ahead of Pole Katarzyna Wasick, with Australian Meg Harris and American Erika Brown tied for bronze.
The Swede took her first European title at 14 and her first world title a year later in 2009. This was her 20th world championship medal.
"Maybe my mind-set and also a lot of hard work, but also I love what I do," she said of her longevity.
Sjostrom narrowly missed another medal when she anchored Sweden to fourth in the women's 100m medley relay that closed the championships.
"It's been a busy four days for me," she said. "I feel like it's business for me too, I just go in and do my job I guess."
The United States won, anchored by 17-year-old Claire Curzan. Australia were second and Canada, with Penny Olesiak holding off Sjostrom, third.
The men's 50m backstroke gold medal was presented twice, with the US anthem played twice.
In the first race of the evening, Justin Ress was disqualified after video review for finishing entirely under water as he touched the wall first.
Mr. Ress training buddy Hunter Armstrong was awarded gold, winning in 24.14 seconds.
Ksawery Masiuk, a 17-year-old Pole, initially took silver, 0.35sec back, with Italian Thomas Ceccon, who set a 100m backstroke world record on Monday, taking the bronze on loan.
Mr. Armstrong wiped a tear away as he stepped off the podium after accepting the gold in the evening's first medal ceremony.
"I'm very disappointed my team-mate was disqualified and hopefully Team USA's protest will be successful," Mr. Armstrong said.
He got his wish, when a jury upheld the appeal. Mr. Ress came out alone to stand on the top step of the podium and receive his medal in the last medal ceremony of the championships.
Ceccon had taken pre-emptive revenge by swimming the breaststroke leg as Italy edged the Americans, the reigning champions and world record holders, in the 100m medley relay final. Britain were third.
That was a fifth gold for Italy after Gregorio Paltrinieri earlier swum the second fastest time in men's 1500m freestyle history to win his third world title in the distance.
The 27-year-old Italian surged away from the start, setting a breakneck pace. He was on world record pace for much of the race before fading at the end to finish in 14min 32.80sec and miss Sun Yang's mark by 1.78sec.
American Bobby Finke was second, 3.90sec back, with Florian Wellbrock third at 4.14. Paltrinieri said he had been motivated by finishing fourth out in the 800m
"I came out with the mindset that I wanted to destroy the pool," he said after becoming the oldest ever 1500m world champion.
"I'm 28 in a couple of months," he said."But I'm still learning"
Lithuanian Ruta Meilutyte won her first world gold since 2013 when she edged Italian 17-year-old Benedetta Pilato by 0.10sec in the women's 50m breaststroke final. South African Lara van Niekerk was third.
Meilutyte had not won a major championship medal of any colour since 2015. "It's nice to be a world champion," she said.
