Ole Gunnar Solskjaer was over the moon with the contribution of Brandon Williams after the teenager finished his full Manchester United debut on the winning side.
Williams, 19, and 18-year-old James Garner were two surprise picks for United's Europa League visit to Partizan Belgrade on Thursday.
Playing at left wing-back, Williams completed all 90 minutes of the Group L match while Garner started alongside Scott McTominay in midfield before being withdrawn for Andreas Pereira with nine minutes remaining.
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A single strike from the penalty spot from Anthony Martial was enough to give United all three points, in the process sealing their first away victory since beating Paris Saint-Germain in March.