Needing at least a draw to have a chance of progressing into the play-offs, Wales were undone by a resolute Republic of Ireland, who soaked up pressure, scored on the break through James McClean on 57 minutes and then defended for their lives to hold on to the 1-0 win.
It was a rare home defeat in qualifying for Wales in recent years and left them third in European qualifying Group D. Serbia beat Georgia to book their place in Russia next summer while the ROI now await their play-off opponents with matches played next month.
Ben played the full 90 minutes in Cardiff.