A stunning late goal from Tommy Hope sent MK Dons through to the Fourth Round of the FA Youth Cup for the very first time.
After an excellent defensive performance and some fantastic goalkeeping from Alfie Jones, centre-back Hope broke the deadlock with superb half-volley on 87 minutes - a goal which made history for the young Dons.
Edu Rubio’s side will now face either Colchester United or Crewe Alexandra in the Fourth Round.
The first chance of the game fell the way of Liam Sole on six minutes. The winger climbed well to meet David Kasumu’s free-kick but his header was gathered by George Ratcliffe.
Ryan Reynolds then headed off target for the visitors before his teammate Sion Spence put an effort wide of the left post from close range - the best chance of the opening quarter of an hour.
Both sides enjoyed spells of possession during the next 15 minutes but neither side created a goalscoring chance until Cardiff were awarded a free-kick just outside the D at the half-hour mark. Sam Bowen took the set-piece but his goal-bound effort was kept out by a terrific diving save from Alfie Jones.
That stop ensured the score remained goalless at the break although Isaak Davies went close to changing that seven minutes after the re-start, shooting just wide from inside the area.
On 56 minutes, Jones pulled off another fantastic save, this time to deny Reynolds - the first-year scholar got down well and stopped the header with a strong right hand.
Jones enjoyed a superb hour between the sticks and in the 62nd minute he tipped wide a strike from Connor Davies before he pulled off an even better save from the resulting corner to prevent his side falling behind.
The first-year scholar was called into action again on 66 minutes to keep out Sam Parsons’ header. Spence pounced on the loose ball inside the area but he was denied by a superb sliding block from Tommy Hope.
Rubio’s men had defended well all game but were being frustrated by Cardiff at the other end of the pitch.
They did, however, almost create an opportunity for a late winner in the 84th minute but Bradley Bell’s cross was just too high for Charlie Pattison.
That chance seemed to ignite the Dons, who came forward again on 87 minutes and were awarded a free-kick for a foul on Kasumu.
Bell delivered into the area and the ball eventually found its way to Hope, who sent a superb half-volley over the Bluebirds goalkeeper and into the net via the crossbar - a stunning way to give his side a late lead. 1-0.
Jay Bird went close to doubling the lead soon after the re-start with a curling shot from Liam Sole’s pass.
Cardiff had one final opportunity after being given a free-kick deep into stoppage-time. However, the Dons survived the threat to secure a dramatic victory at Stadium MK as well as a place in the Fourth Round of the FA Youth Cup.
Starting XI: Jones; Ackom (Hourican-Harvey 74), Tapp (c), Hope, Sorinola (Wright 80); Pattison, Kasumu; Bell, Bird, Sole; Martin (Evans 59).
Unused subs: Rose (GK), Brennan.
Goal: Hope (87)