In the first of a double-header against Portugal, Wales went down to a 90th-minute volley from defender Carole Costa in Rio Maior.
Manager Jayne Ludlow gave former U-19 captain Ffion Morgan her first senior start, Elise Hughes (17) played centre midfield, while Gemma Evans made her first start since the Cyprus Cup in March.
With the rain falling heavily in the first half, Wales found themselves with their best chance of the game as Kayleigh Green pestered the Portugese back line, forcing an opportunity for Natasha Harding who saw her chipped attempt land just wide of the goal.
In the second half it was Harding again that found herself in front of goal, this time meeting a through ball from Helen Ward but her drilled strike found the hands of goalkeeper Ines Pereira.
Ludlow brought on 18-year-old Ella Powell for her senior debut to lead the attacking line alongside 20-year olds Kylie Nolan and Hannah Miles. Megan Wynne had her first Wales outing since 2013 and the full back seized on the opportunity to push the team forward for a winning goal.
Despite the pressure from the Welsh youngsters, Portugal also pushed for a winner and from a corner in the final stages, a scrambled clearance landing at the edge of the box and Carole Costa found the roof of the net with a stunning volley.
Ludlow told faw.cymru: “It was a great performance and we were unlucky to concede at the end. We had great shape throughout and everyone gave a good performance. Hopefully we can build on that for Tuesday’s match.”
The second game on 13th November is at 3pm local time in Cova da Piedad.
Portugal – Ines Pereira, Diana Gomes, Silvia Rebelo, Carole Costa, Dolores Silva (C), Fatima Pinto (Diana Silva, 59), Monique Goncalves (Jessica Silva, 46), Andrea Norton (Carolina Mendes, 83). Laura Luís (Telma Encarnação, 59), Ana Capeta (Vanessa Marques, 59), Ana Leite (Tatiana Pinto, 83).
Unused Subs: Patrícia Morais, Rute Costa, Mónica Mendes, Matilde Fidalgo, Vania Duarte, Tatiana Pinto, Anita Santos
Wales: Laura O’Sullivan, Ffion Morgan (Megan Wynne, 90), Gemma Evans, Sophie Ingle (C), Nadia Lawrence, Natasha Harding (Ella Powell, 64), Angharad James, Kayleigh Green (Kylie Nolan, 76), Elise Hughes, Hayley Ladd, Ellen Ward (Hannah Miles, 76).
Unused Subs: Claire Skinner, Emma Gibson, Olivia Clark, Cori Williams, Charlie Estcourt, Kelly Isaac, Chloe Williams.
In other internationals, Australia were beaten by Chile, Germany saw off an Italy fightback to win 5-2, France beat Brazil 3-1 and Japan went one better against Norway.
Delphine Cascarino, Elise Busaglia and Wendie Renard scored for the 2019 World Cup hosts, with Brazil replying with a stoppage-time Darlene consolation.
Lina Magull and Alexandra Popp put Germany 2-0 up early on but Italy hit back through Barbara Bonansea and Daniela Sabatino. Giulia Gwinn restored the lead, subs Lena Petermann and Leonie Maier then making sure of the victory.
Emily van Egmond scored early and late penalties for the Matildas but visitors Chile netted three times in-between through Francisca Lara, Carla Guerrero and sub Yessenia Huenteo.
Mana Iwabuchi bagged a brace for the Nadeshiko, Kumi Yokoyama and substitute Yuma Momiki one apiece before Ina Gausdal got one back for Norway.