Montgomerie hit only four boundaries but assumed a general air of command for an unbeaten 86, batting throughout in an innings of 113 balls.
His match winning unbroken stand of 68 with Tim Walton (41no) came in a 10 over spell which galvanised his side.
The temptation to draw grieving comparisons were immense for much of this rescheduled AXA Life contest.
Initially due to be played on the day of the death of Diana, Princess of Wales, the match was cancelled as Earl Spencer is the home Counties patron.
Northamptonshire's lethargy in allowing Durham to reach 185 for 6 before ponderously setting off in reply, befitted a county whose own season is best forgotten. David Boon's unbeaten 54 came off 70 balls and he held Durham together after a second wicket stand of 52 between Stuart Hutton (30) and Martin Speight (26).
Northamptonshire needed 49 from the final seven overs and that asking rate of seven and over still applied with three remaining.
But Walton had altered the shift of the match with successive fours in Alan Walker's sixth over and when he dispatched the same bowler through midwicket to the boundary in the 37th, and was then dropped by John Wood off Neil Killeen in the next, Durham knew their fate.
Durham's frustration at narrowly missing their first away win of any description since August 1995, which ironically came at Northampton was huge.
And Walker's final act of kicking a stump out of the ground was a futile symbolic gesture.