Robbie Neilson read his side the riot act at half time, despite leading 2-0 against Shrewsbury on Saturday.
Having dominated proceedings in the 2-1 win, Neilson was frustrated when his side took their foot off the gas after 20 minutes, already two goals to the good thanks to Kieran Agard and Paul Downing.
After calling for more aggression last week, the boss warned that is they were playing one of League 1's top sides, Dons would have been beaten.
"My big issue at half time was that if we played like that against Sheffield United, Bolton or Scunthorpe, we'd get beaten," he said. "We must make sure we do the things we work on all week, and don't give teams opportunities. We should be sitting here having won 5-0.
"We need to be more ruthless. At 2-0 up, you have to want three, four or five. You do that by doing the same things that got us the success in the first 20 minutes. We slipped back into overplaying and not taking chances to put teams under pressure. We're getting better at it.
"They went back to doing the things we didn't want them to do. Overplaying, not taking opportunities to get the balls into the box and take shots. We have to keep progressing and telling them exactly what we want."
The result though sees Dons climb to 15th in the table, moving eight points away from the relegation zone and back to within 11 points of the top six, and is their first in four games, having suffered a disappointing run of one point from a possible nine.
Neilson added: "It was great to get back to winning ways. The first 15, 20 minutes we were really good, but after that, we were poor and I was quite disappointed. I came in at halftime and had a go at them because I felt we should have capitalised. But in the second half again, it was pretty flat.
"It's a big three points for us, but we want to go to Bradford and win it. I think if we can play like we did in the opening 20 minutes here, then we'll win. But it's all right talking about it, we have to go and do it."
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