As the evening wore on Antonio Conte resembled an increasingly disappointed teacher, apparently saddened by his class’s failure to absorb the basic lessons he had devoted hours to imparting. Tottenham’s manager did not looked entirely surprised when his worst fears were realised and, deep in extra time, the 19‑year‑old Josh Coburn, after only 11 minutes on the pitch, scored a fine, richly deserved winner, propelling Chris Wilder’s impressive side into the sixth round.