The League One leaders ran rings round a second-string Canaries outfit and fully deserved their thumping victory and a place in the third round.
Former Canaries midfielder Luke Chadwick struck twice in addition to goals from Sam Baldock and Daniel Powell to seal the unexpected rout – manager Paul Lambert’s biggest since taking charge two years ago.
Lambert fielded a completely different starting line up to the one that drew one-all with Stoke on Sunday, with the weekend’s daunting trip to Chelsea clearly on his mind.
But there was still plenty of experience in his side and it was certainly a surprise to see them outplayed by a club two divisions below them.
After a quiet start Karl Robinson’s slick passing side grabbed a surprise lead on 21 minutes when Chadwick scored the first of his two goals.
The former Norwich man was put through by Stephen Gleeson and coolly stroked the ball under rookie goalkeeper Declan Rudd to open the scoring.
The Dons doubled their advantage seven minutes later after Adam Drury had carelessly lost possession in midfield to allow Gleeson the space to give Baldock a run on goal.
The highly-rated front man needed no second invitation to have a try from 25 yards and his well-struck shot left Rudd wrong-footed to find the back of the net.
The goals came as a shock, even though Lambert has a poor Cup record at Norwich – but things got even worse for his side after the break.
The game was effectively over as a contest on the hour mark when a brilliant Dons move down the left ended with a slick one-two between Chadwick and Dean Bowditch and a sweet finish from the winger.
The new-look Norwich defence, featuring new signing Daniel Ayala, simply had no answer for the visitors’ slick passing and shot themselves in the foot on 67 minutes when Andrew Surman’s careless pass put in substitute Powell who beat Rudd just four minutes after coming on.
With the game long since lost, Norwich finally began to threaten, with Korey Smith and Simeon Jackson both going close.
But by then the Dons were in the comfort zone as Lambert was left to reflect on his biggest defeat ahead of a trip to Stamford Bridge.