The Dean Court starlets had lost four consecutive Merit League fixtures but bounced back in Buckinghamshire despite a second-half scare.
The hosts opened the scoring early on but efforts from Sam Surridge and Matt Neale put Carl Fletcher’s fledglings in front heading into the break.
Cherries appeared to end the game as a contest with three goals in 10 minutes after the restart as Jack Simpson, Matt Worthington and Surridge registered.
However, Dons mounted an excellent fightback and were just a goal down with 10 minutes left on the clock.
And Cherries had keeper Callum Stanton to thank as he made a top-drawer stop in the closing seconds.
Roach told the Cherries website: “Carl and I had a very mature and strong conversation with the youth team this week about improving their professional levels and expectations.
“They are now in an environment where they need to show a certain standard of football and they have recently been a little short of that.
“Mentally, the MK Dons result was huge for us and it shows that the players took everything on board. They stepped up to the standard we wanted.
“It was an absolutely fantastic game of football from both sides. We could have scored a lot more as it was a very open game.
"When we were 5-2 up we dropped off a little bit, which was frustrating. Consequently, that gave MK Dons a lot more space and it nearly cost us.
“One of the biggest positives from this weekend was the opportunity to promote some schoolboys through the system. This gave them a great chance to mix with the youth team.”