It is just seven months and one day since Michael Laudrup's side lifted the first major honour in their 101-year history with a thumping 5-0 victory over Bradford at Wembley.
But the holders were brought crashing back down to earth by another side who also share fond recent memories of the competition - 2011 winners Birmingham.
It was a classic game of two halves in the third-round tie as the Swans saw plenty of the ball in the opening period and hit the woodwork twice within a matter of seconds through Wilfried Bony and Alejandro Pozuelo.
But the Championship hosts appeared a different animal after the break and Dan Burn headed home his first goal for the club in the 56th minute before Matt Green added a second from close range soon after.
Inspired by winger Chris Burke, who played his part in all three goals, Tom Adeyemi also got in on the act with his maiden goal late on - with Bony netting a consolation with virtually the last touch.
Papiss Cisse's first goal since April helped to ease Newcastle into the fourth round with a 2-0 win over Leeds.
Cisse's drought finally ended 31 minutes into a pulsating encounter when he powered a header past goalkeeper Paddy Kenny to end a run stretching back to the 1-1 Europa League draw with Benfica on April 11.
But the tie remained in the balance until deep into the second half when strike-partner Yoan Gouffran blasted home to wrap up a win over the Championship side.
Leeds gave as good as they got for long periods with powerhouse frontman Matt Smith causing all kinds of problems for defenders Fabricio Coloccini and Mike Williamson - and the visitors were only denied an early lead by the crossbar after Tim Krul saw Ross McCormack's delicate effort sail over him.
But ultimately it was Newcastle's finishing which won the day to the delight of a crowd of 36,220, who united to chant the name of Gary Speed 11 minutes into the game.
Stephen Ireland marked his first Stoke start with a goal as the Potters claimed a 2-0 win over Tranmere.
Former England striker Peter Crouch added a last-gasp second as Mark Hughes' side saw off League One Rovers 2-0 at Prenton Park.
Irish midfielder Ireland, hoping to rejuvenate his career after moving on a season-long loan from Aston Villa, struck midway through the first half with Crouch striking with the last kick of the game.