Mathias Doumbe missed the decisive spot-kick as MK Dons crashed out of the FA Cup after losing their first-round replay to Stevenage 7-6 on penalties.
Boro keeper Chris Day denied the Dons victory in the shoot-out when he saved Peter Leven's penalty, before Doumbe blasted his effort over the bar. Boro substitute Darius Charles had earlier blasted a stoppage-time equaliser to cancel out Lewis Guy's 49th-minute opener for the Dons.
Stevenage bossed the first half and Scott Laird struck the foot of the post with a curling 30-yard free-kick before drilling another shot just wide. Michael Bostwick and Chris Beardsley then both went close, while Jon Ashton's deflected 12-yard strike hit the bar following a Stacy Long corner.
But the Dons improved after the break and Guy put them ahead just four minutes after the restart, racing clear onto Leven's pass to slot past Chris Day for his third goal of the season.
Doumbe and Leven missed good chances to double the Dons' lead before Charles equalised in the fifth minute of stoppage time, lashing home after keeper David Martin had dropped Yemi Odubade's cross.
The Dons dominated extra-time but substitute Daniel Powell dragged their best chance inches wide from 10 yards before their shoot-out defeat.