Juan Familia-Castillo was back in action for Chelsea last night.
Castillo was handed a full 90 by coach Andy Myers.
Oxford's Dan Agyei was first to react to a deflected cross and turned home from close range, completely against the run of play. While Oxford were happy with their lead, Chelsea searched for a response but after a few missed chances the hosts struck again, moments before the break.
An inspired change at the break saw the young Blues earn a goal back - Jon Russell, who scored in this competition against Plymouth last season, found the net shortly before an hour's play. But in the end Oxford held on for the 2-1 win.
Along with Castilla, fellow Dutchman Ian Maatsen featured at the back, while Austria youth international Thierno Ballo led the line.