The young defender, 19, started alongside Jan Vertonghen, captain for the night, as we ran out 1-0 winners against the well-organised Championship side.
Juan, signed in the transfer window from Estudiantes in Argentina, looked unflustered on the night and showed real defensive nous in a couple of potentially tricky situations.
He helped the team keep a clean sheet and Dele Alli’s goal 20 minutes into the second half booked our passage into the fourth round.
Mauricio said: “I'm happy, he's still so young and he needs to feel the game here in England, it's completely different.
“He was so calm and tried to play. He still needs to adapt to everything and he needs time but this evening he showed his talent.”