The Dons were held to a goalless draw in difficult conditions at Vale Park on Saturday afternoon.
The point, however, saw the Dons guarantee at least a play-off place while they also picked up their 22nd clean sheet of the season.
There were three changes for the Dons with Dean Bowditch and Daniel Powell replacing Rob Hall and Lewis Baker, while Joe Walsh came in for Dean Lewington (knee, injured in training Friday). Devante Cole missed out due to the limit of five loan players in a matchday squad.
The first 10 minutes were evenly contested with both sides trying to take an early stranglehold of the game.
From the Dons’ point of view, a couple of Bowditch free-kicks were dealt with by the Vale defence while, at the other end, Walsh did well to mop up in front of Louis Dodds on the quarter-hour mark.
Richard Duffy saw a poked effort deflected behind before Kyle McFadzean was in the right place at the right time five minutes later as the hosts looked to try and make the most of successive corners.
Karl Robinson switched Bowditch and Carruthers with 25 minutes on the clock with the aim to try and bring a spark to the Dons’ attack.
That almost did the trick as a clever pass from Carruthers was just a couple of yards in front of Grigg, who was bearing down on Chris Neal after evading his marker.
The pitch and Vale’s dogged defending was making it difficult for the men from MK1 to gain any fluidity going forward, but they did see a lot more of the ball as the first half drew to a close.
However, it was the hosts who came closest to scoring on the stroke of half-time when Mark Marshall headed Dodds’ delivery wide of the target.
After nice interchange with Frederic Veseli, Dodds scooped over the first effort of the second half, which as a whole started slowly.
Robinson made a double change just past the hour mark with Hall and L Baker coming on for Powell and Dele Alli – L Baker at No.10 and Hall on the right wing.
At the other end, Michael Brown was denied on two occasions from distance before Antony Kay made an important clearance under pressure on 65 minutes.
Vale substitute Mohamed Coulibaly flashed a shot narrowly past the top left-hand corner after a clever turn with 20 minutes remaining.
The game began to become stretched as it entered the final 15 minutes but the Dons were still finding it hard to get past a Valiant home defence.
A clever run from Hall won the Dons a free-kick and gave them hope although it was comfortably cleared on 82 minutes.
The lively Hall was beginning to threaten down the right-hand side and only some last-ditch defending denied the Bolton Wanderers loanee creating a clear-cut opportunity for a team-mate.
Robinson’s side continued to try and find a winner, but they would have lost it in the final minute if it wasn’t for a goal-line clearance from Lee Hodson after the hosts had broken down the right.
MK Dons: Martin; Hodson, McFadzean, Kay, Walsh; Potter (c), Alli (L Baker 60); Bowditch, Carruthers, Powell (Hall 60); Grigg.
Unused subs: Burns, Spence, Green, Hitchcock.
Bookings: Potter, Carruthers, Walsh.
Attendance: 4,379 (383 Dons fans).