Wales manager John Toshack admitted his young side was no match for Group Six leaders Poland despite the narrow loss.
Said Toshack after the 1-0 defeat: "The England game on Saturday took a lot out of my players physically and mentally.
"Then to have to come to Poland and play the best team in the group on such a difficult occasion was a bit too much for some of my lads.
"We've come up a bit short in both games. Poland are a very good side and we did our best, but they were better."
Maciej Zurawski coolly converted a 53rd-minute penalty in Warsaw to clinch the three points that moved them to within one more of a place in the 2006 World Cup finals in Germany next summer.
Zurawski had a penalty saved against Austria in their previous game on Saturday, but Poland manager Pawel Janas said he had every faith in the Celtic striker.
"Wales had nothing to play for and we have executed our ideal plan," said Janas.
"My heart didn't tremble for a minute when Maciej set up the spot kick. We agreed beforehand he would take it and he did it perfectly."
Poland's players and fans thought the result would be enough to assure them of an automatic place in the finals a but Sweden's late winner over Hungary means they will have to wait.
If the Swedes had dropped points it would have guaranteed that Poland would finish with at worst as one of the two best runners-up from the eight European groups.
"We're just left feeling a bit empty," Janas added.
Wales' starting XI had an average age of 25, and that dropped even lower with the second half introduction of Richard Duffy - who gave away the penalty - Craig Davies and debutant Joe Ledley.
Toshack said the game would prove to be invaluable experience for the youngsters as he continues to build for the next European Championship qualifiers.
He said: "For some of our lads playing in the lower divisions this was an experience they have never faced before.
"I can't blame them, they did their very best out there, but this Poland side are the best team in the group and it showed.
"Some of our lads did not play their best, but I can't blame them for that in these conditions."