Ole Gunnar Solskjaer made eight changes to the Manchester United team that beat Sheffield United 3-0 in the Premier League on Wednesday, and his team produced a largely listless performance against the Premier League's bottom club.
It was, in fact, Norwich who had the best of the chances in a listless first-half, and would have went to the interval with the advantage had it not been for a fine last-ditch block from Harry Maguire to deny Lukas Rupp.
Ighalo gave United the lead just moments into the second half, acrobatically stabbing home from close range after good work from Luke Shaw and Juan Mata.
The Canaries almost levelled the tie with 20 minutes left but Ben Godfrey appeared to direct an Alexander Tettey goalbound effort off the line – however, their perseverance would be rewarded when Todd Cantwell took aim from 25-odd yards to send the tie to extra time.
However, Daniel Farke's men would have to take on the challenge of an extra 30 minutes after Timm Klose was sent off for a foul on Ighalo.