Hopes of retaining the Vertu Trophy for the third season in a row over following defeat in Wiltshire.
Peterborough United will not be visiting Wembley in the Vertu Trophy final in 2026 after being knocked out at the Round of 32 stage by Sky Bet League Two side Swindon Town at the County Ground.
A goal three minutes from time by Ollie Clarke secured a 1-0 win for the Robins at the end of a game where, what chances were created, came the way of Luke Williams' side who were wasteful in front of goal.
Substitute Gustav Lindgren was superbly denied by Swindon goalkeeper Lewis Ward while Brandon Khela fired over in stoppage time as Posh suffered a third straight defeat in all competitions.
It wasn't a game flush with clear-cut opportunities, particularly in the first half with an effort from Harry Leonard, which went wide, the only real moment of quality.
At the other end, Posh defended well and restricted the hosts to just half-chances with Alex Bass largely inactive in the Posh goal.
Lindgren's chance was created by himself, but his low left-foot shot was superbly repelled by Ward at full stretch, down to his left.
The goal arrived on 87 minutes with midfielder CLARKE timing his run into the box to perfection before slotting his shot past Bass and into the bottom corner.
Substitute Khela fired over at the back post deep in stoppage time as Posh tried to find an immediate riposte, but it was not to be as the Robins continued their fine season with progress in the trophy.
Swindon Town: Ward, Wright, Ball (sub Nichols 57min), Glatzel (sub Snowdon 57min), Kilkenny (sub Clarke 57min), Munroe, Bodin (sub Tabor 57min), McGregor, Oldaker (Drinan 46min), Knight-Lebel, Ehibhatiomhan. Unused subs: Ripley, Gray.
Posh: Bass, Johnston, Collins, Odoh, Frith (sub Lisbie 64min), Woods (sub O’Brien-Brady 75min), Mills, Okagbue, Leonard, Garbett (sub Lindgren 75min), O'Connor. Unused subs: Reyes, Dornelly, Lolos, Khela.
Half-time: Swindon Town 0-0 Peterborough United
Full-time: Swindon Town 1-0 Peterborough United
Attendance: 2,135 (239 Posh fans)
Referee: Dale Baines