Newport County suffered heartbreak as Wimbledon won 5-4 after penalties.
A sublime curled finish by Yahya Bamba put County in front, with the Exiles believing that they had done enough to secure victory.
However, a last-minute equaliser from Callum Maycock saw the game go to a penalty shootout.
Steve Seddon scored the Dons' winning penalty as Matt Smith's penalty was saved.
Newport County started brightly at Plough Lane, with Bamba coming close to opening the scoring inside the early stages.
Bamba found himself inside the penalty area and looked to use his tricky footwork to create an opening, but AFC Wimbledon defender Ryan Johnson stood firm to keep the County forward at bay.
The hosts soon threatened from a set-piece, sending a dangerous corner into the County penalty area, but Jordan Wright commanded his box brilliantly to claim the delivery and relieve the pressure.
Wimbledon continued to test the County defence, with James Tilley firing a threatening effort towards goal, but Wright was equal to it, making a strong save between the sticks to keep the scores level.
County remained organised at the back as both sides continued to search for the opening goal.
A quarter of the way through the first half, Bamba showcased his ability once again, skipping past Ryan Johnson with some outstanding trickery before being brought down moments later, earning the Exiles a free-kick in a promising position.
Cameron Evans tested Nathan Bishop from range, but his effort lacked the power to trouble the Wimbledon goalkeeper, who comfortably gathered the shot.
Harrison Biggins unleashed a volley from just outside the penalty area, with his effort taking a deflection off a Wimbledon defender and going behind for a County corner.
Seddon came close for the hosts as a dangerous ball dropped inside the penalty area, but the Wimbledon man in blue was unable to make the crucial connection.
Tom Davies fired a dangerous ball into the mixer, where Christian Doidge rose highest, but his header was just off target.
On the stroke of half-time, the hosts came close to breaking the deadlock through Aron Sasu, but it was wonderfully stopped by Wright in goal, keeping the scoring level.
County started the second half on the front foot, with some neat build-up play between Ciaran Brennan and Biggins creating an opportunity for Shaquille Gwengwe, but the forward was unable to find the net with an awkward turn.
A massive chance came for the Exiles as an inviting corner dropped to Lee Jenkins, but his close-range effort was saved.
Bamba provided another crucial counter, using his pace to skip past the Wimbledon defender before winning a corner for the Exiles.
Chances couldn't get closer for Newport as Gwengwe's penalty attempt was saved and cleared away.
However, Bamba found the opening goal with 20 minutes to go as his audacious curling effort found the top right corner.
The hosts applied significant pressure during the latter stages, but Wright stood firm in the County goal to keep the Exiles in front.
But the hosts levelled the scoring in injury time as a short-range effort was taken by Callum Maycock, who was able to find the net.
Although County never fell behind, they fell short at the last kick of the game as Seddon converted his penalty to win Wimbledon the game.
Although County never fell behind, they fell short at the last kick of the game as Seddon converted his penalty, with the hosts progressing to the second round.
Newport County: Wright, Evans (Smith 85’), Davies (Merritt 84’), Cameron, Jenkins, Brennan, Gwengwe (Alexander-Walker 72’), Biggins, Bamba (Sassi 75’), Norman, Doidge (Garner 72’)
Substitutions: MacDonald, Patten, Pugh, Jarvis
AFC Wimbledon: Bishop, Seddon, Johnson, Tilley, Nelson (Maycock 65’), Browne, Smith (Hackford 81’), Hippolyte, Sweeney (Stockley 65’), Sasu (Sessegnon 65’), Ogundere
Substitutions: McDonnell, Reeves, Harrison, McCoy-Splatt, Jennings.
Officials: Paul Howard (Referee), Alex Bradley, Conall Bartlett (Assistant Referees), Nick Blogg (Fourth official).
Attendance: 3766.