Ricardo Batista and Beatrice Mallozzi secured junior glory at the World Triathlon Series (WTS) Grand Final with sprint finishes in Lausanne.
Portuguese Batista described his victory as unbelievable, after outsprinting Australian Lorcan Redmond in the final 300 metres to claim gold.
He said: "I have trained very hard and long for this, since my first year as a junior.
"I was worried on the bike course because we had too many athletes in our group, so I was just trying to stay safe and save some legs.
"And then out of T2 I felt really strong and was able to drop many athletes."
Italy's Alessio Crociani led the men's race out of Lake Geneva, with Jamie Riddle of South Africa and Britain's Marcus Dey in hot pursuit.
Batista was 10 seconds back going into the four-lap bike course.
A group of 32 riders entered the second transition, with Czech Republic's Radim Grebik and Switzerland's Sasha Caterina leading the pack.
Australian Joshua Ferris moved to the front, before Batista accelerated on the climbs.
Batista edged ahead of Ferris and Frenchman Boris Pierre, with Redmond in hot pursuit.
In the closing stages, just Batista and Redmond were left to contest the gold medal, and the Portuguese had the legs to sprint clear, winning by almost 10 seconds.
Spain's Sergio Baxter Cabrera held off Pierre to claim bronze.
In a striking sprint finish Beatrice Mallozzi from ITA is crowned Junior World Champion in Lausanne! 🥇#WTSGrandFinal— World Triathlon (@worldtriathlon) August 30, 2019
Silver to Costanza Arpinelli ITA 🥈
Bronze to Jessica Fullagar FRA 🥉
The action is LIVE at https://t.co/dToUk2wdD4
Photo by @DellyPhotoNinja #WTSLausanne pic.twitter.com/AmVlZMeM4s
Batista clocked 55min 05sec for gold, with Redmond second in 55:12, and Baxter Cabrera in third place in 55:16.
In the women's race, Mallozzi looked in some discomfort, clutching her stomach in the closing stages, before gritting her teeth and surging past training partner Costanza Arpinelli to take the junior title.
A false start saw the triathletes climb back onto the pontoon for a restart.
Portugal's Gabriela Ribeiro led a group of five out of the water and onto the bikes in Lausanne.
Two packs formed, with Hong Kong rider Bailee Brown at the head of an 18-strong group, with Swiss rider Anja Weber attempting to string out the field in the early stages.
Mallozzi was in the chasing group of 17 riders who cut the gap down to 20 seconds over the four-lap bike section.
As the run began, Jessica Fullagar of France pushed the pace as Mallozzi, Arpinelli and Hannah Knighton of New Zealand kept close attention.
The efforts of Knighton and Fullagar on the bike proved costly as they wilted on lap two.
Arpinelli was in the box seat for gold with 500m to go, as Mallozzi held her stomach, but the European junior champion found an extra gear to sprint past her compatriot for glory in 1:00.41.
Arpinelli took silver in 1:00.42, with Fullagar in bronze in a time of 1:00.53.
France's Emilie Morier won the women's under-23 title in 2:04.01 as Oliva Mathias of Britain finished second in 2:04.08.
The bronze went to German Lisa Tertsch in 2:04.32.
Roberto Sanchez Mantecon of Spain claimed glory in the men's under-23 race, clocking 1:50.20 in topping the podium.
Hungarian Csongor Lehmann was second in 1:50.36 as Ran Sagiv of Israel took the last step on the medal rostrum in 1:50.50.
The elite men's and women's races are tomorrow.