Dons and Northampton Town will replay in the Emirates FA Cup after the third-round tie at Sixfields ended in a 2-2 draw.
However, Nicky Maynard got the final touch on a Ben Reeves’ cross to ensure the Dons’ place in the hat for the fourth round.
Cody Cropper and the returning Jake Forster-Caskey started in place of David Martin and Darren Potter, who are carrying knocks, while Academy player Callum Brittain was named on the bench for the first time.
The Dons were the first to threaten on three minutes when Dean Bowditch broke and fed Rob Hall, who drove goalwards and forced Adam Smith into a fine stop from 25 yards.
Northampton’s opening chance came a minute later, Nicky Adams heading Ricky Holmes’ cross into the arms of Cropper.
Karl Robinson’s men took the lead on 13 minutes when Ryan Cresswell put Lee Hodson’s teasing cross into his own net – Bowditch did get a touch but the ball looked to be already over the line.
An opportunity for either side followed shortly afterwards – Adams seeing a shot well blocked by Joe Walsh while Hall dragged a low drive wide of the target from the edge of the area.
The Dons then weathered a mini spell of pressure from the hosts before beginning to assert themselves 25 minutes in, which included a shot from Reeves.
McFadzean breathed a huge sigh of relief on 33 minutes when a cross was flicked on and he headed narrowly past the post, prior to Sam Hoskins scuffing a shot wide from 15 yards.
Chris Wilder’s men were enjoying the lion share of territorial advantage but the Dons fired a warning shot on 42 minutes when Murphy drove an effort just wide.
The hosts were level on 49 minutes, Holmes curling home a fine 20-yard effort - Cropper had no chance.
Holmes doubled his tally for the afternoon and put the Cobblers ahead on 58 minutes, receiving the ball from Adams and drilling past Cropper from 12 yards.
Robinson responded with a triple substitution – Matt Upson, Samir Carruthers and Nicky Maynard replaced McFadzean, who is on nine bookings, Murphy and Church.
A kind deflection gave Maynard an opportunity but, as he went to pull the trigger, he was challenged by Rod McDonald – the Dons wanted a penalty but the referee waved away the strong appeals.
Ryan Cresswell headed over his own bar before Adam Smith was forced to punch clear a corner as the Dons enjoyed a spell of pressure with just under 20 minutes remaining.
The Cobblers had to clear a dangerous cross prior to Hall testing Smith from a 25-yard free-kick and then sending an effort over the top.
Their pressure told and they were level on 82 minutes when Maynard got the final touch on a driven ball into the box by Reeves, setting up an interesting finale.
However, neither side could force a winner and the two will meet again, this time at stadiummk.
MK Dons: Cropper, Spence, McFadzean (c) (Upson 61), Walsh, Hodson; Forster-Caskey, Reeves; Bowditch, Hall, Murphy (Maynard 61); Church (Carruthers 61).
Unused subs: Burns, Brittain, Randall, Hitchcock.
Attendance: 5,878 (947 Dons fans).
Referee: Darren Drysdale.