The Dons moved to within three points of top spot in Sky Bet League 1 with a comfortable 2-0 victory over Barnsley.
Karl Robinson’s side have the chance to go abovea the pair when they travel to Scunthorpe United on Tuesday night.
There were two changes to the Dons’ starting XI as Darren Potter and Daniel Powell replaced Samir Carruthers and Ben Reeves, who missed out due to a hamstring complaint.
Dean Bowditch, operating in the No.10 role, almost handed the Dons a fourth-minute lead but, after latching onto Grigg’s pass and beating keeper Ross Turnbull, George Williams cleared off the line.
The Tykes threatened on 10 minutes when David Martin pushed Milan Lalkovic’s cross-cum-shot away – George Waring header over the rebound.
Lalkovic then tried to pick out Alex Kiwomya, who was well thwarted by Alli at the crucial time 12 yards out while, at the other end, Carl Baker shot wide of the target from the edge of the box.
Some outstanding defending from Kyle McFadzean denied Barnsley the opening goal on 25 minutes, getting back quickly to deny Lalkovic the chance to cross for Waring, who was unmarked 12 yards out after a swift counter.
Powell forced Turnbull into a smart save after receiving the ball from the impressive Alli, who then hit the post with a fine effort following some fancy footwork on 33 minutes – Grigg tapped home the rebound but the offside flag was up.
The last action of a fairly uneventful first half saw Waring head Conor Hourihane’s free-kick onto the roof of the net as the sides went in on level terms.
Both teams wasted chances at the start of the second half as Powell’s cut-back couldn’t pick out a team-mate while, at the other end, Ben Pearson fired high and wide.
In truth, it was the visitors who were looking the more likely to break the deadlock and only a last-ditch interception from Antony Kay denied Lalkovic’s cross finding a fellow Tyke on 49 minutes.
However, the boy wonder, Alli, found the breakthrough on 57 minutes, controlling the ball on his chest before firing in off the post from the edge of the box – already his 12th goal of the season.
Bowditch came close to doubling the Dons’ lead shortly afterwards when he curled an effort just wide.
The second goal did arrive on 63 minutes, and it came in some style too. Grigg brilliantly chested down Baker’s ball, flicked it over his marker and expertly rounded the keeper before slotting into an empty net. Watch out for the celebration!
Robinson, in constant contact with Richie Baker from the Directors’ Box, introduced Jonson Clarke-Harris and Devante Cole, the latter for his Dons debut, a minute later in place of Powell and Bowditch.
Baker and Clarke-Harris both saw fierce shots saved as in the Dons went in search of a third, while Grigg also brought a stop out of Turnbull after the Tykes had failed to clear a cross.
Danny Green, the Dons’ final substitute, almost created a third when he whipped in a dangerous cross which Grigg didn’t quite get enough on and the ball rolled agonisingly past the post with just over five minutes remaining.
A fantastic block denied Cole a debut goal against his former club in the closing stages as the hosts continued to threaten up until the final whistle.
MK Dons: Martin; Spence, Kay, McFadzean, Lewington (c); Potter, Alli; Powell (Cole 64), Bowditch (Clarke-Harris 64), Baker (Green 70); Grigg.
Unused subs: McLoughlin, Baldock, Hodson, Carruthers.
Goals: Alli (57), Grigg (63).
Attendance: 8, 310.