A superb first-half showing helped the Dons to a 3-0 success over rivals Peterborough United at stadiummk.
The midfielder doubled his tally with a stunning strike on the stroke of half-time, which all but settled the contest.
Karl Robinson’s men continued to dominate in the second period as they maintained their place in the automatic promotion places.
There were two changes for the Dons – one tactical and one enforced – as Samir Carruthers and Reeves came in for Dele Alli (knee) and George Williams.
The men from MK1 made a blistering start and went ahead as early as the fourth minute when Daniel Powell brilliantly beat Michael Bostwick and set up Grigg, who coolly fired under Ben Alnwick from 15 yards. 1-0
Powell & co continued to cause problems for the Posh defence while, at the other end, Kyle McFadzean threw himself in front of shot from Erhun Oztumer.
Reeves, starting his first game since returning from injury, almost found Grigg but his incisive pass was just too long for the striker as the clock ticked towards the 20-minute mark.
Oztumer rattled the upright from 25 yards shortly afterwards as the visitors momentarily threatened before Powell mis-kicked from a Reeves cutback as the Dons went in search of a second.
Alnwick had to be alert to save a low drive from Grigg after more excellent Dons build-up, but the lead was eventually extended on the half-hour when, after a well-worked short corner between Reeves and Baker, the former drove home from the edge of the area. 2-0
It was almost 3-0 on 40 minutes but the lively Powell fired into the side-netting after more good work from Baker, who himself flashed an effort across the goal five minutes before the break.
The third did arrive on the stroke of half-time and it came in some style too - Reeves curling a magnificent effort into the top left-hand corner to cap a sensational first-half showing from Robinson’s men. 3-0
The second half started in lively fashion with Marcus Maddison and David Norris going close for the visitors and Grigg seeing a shot deflected into the arms of Alnwick after a quick break.
Grigg headed over a Reeves cross from the right wing as the Dons went looking for a fourth, but Posh were still carrying a threat of their own but were finding it difficult to create any clear-cut chances.
Antony Kay headed a Baker corner wide of the target with just over 20 minutes remaining as the men from MK1 maintained a good level of control of proceedings.
Pressure from Grigg and Powell forced Alnwick into a mistake and substitute Williams pounced on the loose ball, but his shot was saved and Baker’s follow-up was just the wrong side of the post.
Williams had a shot cleared off the line by Bostwick after Alnwick has pushed away Baker’s teasing cross and Lewington headed wide as the Dons kept up the pressure.
Substitute Devante Cole saw a shot deflect narrowly off target and Williams forced a smart stop from Alnwick in injury-time but the three goals in the first half did the damage.
MK Dons: McLoughlin; Spence, Kay, McFadzean, Lewington (c); Potter, Carruthers (Andrews 78); Powell (Cole 84), Reeves (Williams 69), Baker; Grigg.
Unused subs: Burns, Hodson, Andrews, Green, Cole, Hitchcock.
Bookings: Andrews, Lewington.
Goals: Grigg (4), Reeves (30 & 45).
Attendance: 11,162 (1,800 away)