Britain were invited to guest at the event in Lisbon and they showed their strength by claiming the top four places in the girls’ competition.
Denton (pictured), on her international debut, took silver, with Mitchell fourth.
The event was won by Emma Whitaker, with Kamie Lowe claiming bronze.
Mitchell clocked the quickest time in the opening swimming event. She touched in 2:13.90, with Denton recording 2:27.85.
In the laser-run, held in sweltering conditions, Denton excelled to move up from fifth to second and overtake Mitchell, who has enjoyed a highly-successful start to 2017.
The competition was part of a week-long training camp in Portugal for the Great Britain Under-17 squad.
Pentathlon GB’s pathway manager Stuart Mason said: “It was a great experience for our athletes to compete in this competition, particularly off the back of our first under-17 ranking competition last month.
“Six of our eight athletes have not experienced running in heat like this before so it’s a fantastic learning experience for them to see what it’s like competing in competitions outside the UK.”