There were mixed fortunes for United on the opening day of the Aegon Future Cup in Amsterdam, although victory over Besiktas on Sunday can still land a semi-final place.
The Reds started the competition with a 2-0 victory against Desportivo Brasil. Jake Cooper, one of two guest players from Reading's Academy, headed home from a corner and an own goal by Lucas Costa, following a Luke Grimshaw cross, secured the points.
The second match was against hosts Ajax and a goal at the start of the second half accounted for Paul McGuinness' side. Although Kieran O'Hara made one stunning stop to thwart Queensy Menig, United were on top in the first period without creating too many opportunities, even if captain Mats Daehli was denied by a flying save after a good run by Grimshaw.
On 33 minutes, Sheraldo Becker raced clear on the right to tee up Elton Acolatse, who tapped into an empty net for the winner. Joe Rothwell saw a fierce shot blocked and Aaron Tshibola, the other Reading youngster, was unable to convert an inviting centre by Grimshaw.
Several stoppages for injuries did not help the Reds' cause as there was little flow to the second half, with the matches only lasting an hour in total.