City youngsters progress in FA Youth Cup
The young Canaries started brightly and took an early lead when Ashley-Seal fired a low shot into the far corner of the Sunderland net.
Glenn Middleton had a chance to double their advantage shortly after but could not control with his weaker right foot when free in the penalty area.
A dangerous cross from the right from City's Jamal Lewis seemed to spark the hosts into life, as they broke away quickly to set Andrew Nelson through on goal but he shot wide under pressure from Callum Ellesley.
Daniel Pybus had a low drive collected well by Aston Oxborough, before a well-worked corner routine drew another fine save from Oxborough after Eliot Embleton's shot.
However, the Black Cats were level moments later through Nelson after he wriggled through the Canaries defence and poked the ball under Oxborough.
As both teams sought the much-needed lead to prevent extra time and penalties, it would be City who took full advantage of an open and entertaining game.
An exquisite cross from Middleton from the left teed up an unmarked Ashley-Seal to double his and his side's tally for the night from six yards with 20 minutes remaining.
Ashley-Seal then broke free and was felled in the Sunderland penalty area moments later, with Todd Cantwell stepping up to dispatch the spot kick expertly.
The City striker would round off the scoring with eight minutes to go when he beat the offside trap and slid the ball under the onrushing Greg Purvis to cap a memorable night.
NORWICH CITY: Oxborough; Ramsey, Ellesley (Wallace, 23), Crowe (c), Syme; Pollock, McIntosh; Lewis, Cantwell (Sambu, 83), Middleton; Ashley-Seal (Couzens, 86). Subs not used: Hale-Brown (GK), Flemming.