The day started badly for Thorup after winger Jonathan Rowe withdrew from the Canaries squad on Saturday morning amid speculation French giants Marseille had submitted a bid to sign the 21-year-old.
Callum Doyle, on loan from Manchester City, was selected by the Dane at left-back on his Norwich debut as both sides matched up in a 4-3-3 formation.
The U’s, however, made the brighter start and Harris somehow managed to misjudge Tyler Goodrham’s low cross with the goal gaping although the linesman’s flag had already been lifted.
Former Norwich man Przemyslaw Placheta then went close for United but saw his near-post strike kept out by Scotland international Gunn.
Harris missed another presentable chance after a cross from the stand-out Long, whose combination with Goodrham caused debutant Doyle problems all afternoon.
The second half brought much of the same and Brannagan saw a deflected effort hit the bar after Norwich failed to clear a Will Vaulks corner.
Barely five minutes later Brannagan made no mistake from Long’s cut-back to seal a terrific return to the second tier for Des Buckingham’s side.
Judging by today’s performance, United may have higher expectations than just safety this season.