A late volley from Carole Costa saw Portugal edge Wales in the first game of their women's friendly double-header at the Municipal Stadium Rio Maior.
Wales manager Jayne Ludlow opted to rest stars Jess Fishlock and Loren Dykes for the mini-tour.
That saw forward Ella Powell, 18, win her first senior cap, although senior striker Tash Harding went closest with a lobbed attempt just wide.
But just as it looked as though Wales would claim a draw, Costa struck.
It was Wales' first game since missing out on a place at next year's Women's World Cup finals.
Wales play Portugal again on Tuesday, 13 November at the Municipal Stadium Cova De Piedade.
Wales squad: Laura O'Sullivan (Cardiff City Ladies), Claire Skinner (Cardiff City FC Women), Olivia Clarke (Nettleham Ladies), Emma Gibbon (Tottenham Hotspur), Sophie Ingle (Chelsea Women), Hayley Ladd (Birmingham City Ladies) Rhiannon Roberts (Liverpool Women), Gemma Evans (Bristol City WFC), Natasha Harding (Reading Women), Angharad James (Everton Ladies), Kylie Nolan (Cardiff City Ladies), Nadia Lawrence (Cardiff City Ladies), Helen Ward (Watford Ladies), Kayleigh Green (Brighton & Hove Albion WFC), Charlie Estcourt (Reading Women), Hannah Miles (Cardiff City Ladies), Cori Williams (Cardiff City Ladies), Kelly Isaac (Cardiff City Ladies), Megan Wynne (Tottenham Hotspur LFC), Emma Jones (Unattached), Grace Horrell (Cardiff City Ladies), Ella Powell (Georgia State University), Elise Hughes (Everton Ladies), Chloe Williams (Wolverhampton Wanderers WFC), Ffion Morgan (Cardiff City Ladies), Tamsyn Sibanda (Arsenal Ladies)