Joao Felix's first-half strike proved decisive, with the Portugal forward's long-range attempt taking a deflection off Ben Davies before wrongfooting goalkeeper Danny Ward.
Wales were forced to withstand sustained pressure for much of the contest, although Craig Bellamy's side showed determination throughout. Their best spell arrived in the closing 15 minutes, when they mounted a strong response and fashioned chances to level the score.
Brennan Johnson went closest to finding an equaliser when his effort struck the crossbar. Lewis Koumas then saw a rebound denied by a vital last-ditch intervention from Rúben Dias.
Ampadu acknowledged the frustration within the Wales camp following the setback and urged the squad to raise their level in the matches ahead.
"We know it was going to be a tough game against very good opposition with a lot of quality, which they showed at times," Ampadu told BBC Sport.
"We knew we were going to have to suffer but we wanted to come here and make a real statement and impact. We wanted to show what we can do on the ball, which at times we did. But we can do a little bit more."
"We're always going to work hard, as we've shown over a countless number of years now. There were a couple chances at the end where maybe we could have got a goal, and then that makes it a better feeling, It's never nice to lose."
