Gregor Buchanan's double and goals from Ross MacLean, Ryan McGeever and substitute Eoghan Stokes gave The Sons their biggest win of the season so far.
Montrose were unable to take full advantage of league leaders Queen's Park's draw with Airdrieonians as they were also held at Cove Rangers. Rory McAllister put Cove ahead early in the second half but Graham Webster equalised from the penalty spot just after the hour mark. The hosts had Blair Yule sent off but saw out the final quarter of an hour to earn a deserved point.
Goals from Euan Henderson and Conor Sammon saw Alloa defeat Falkirk 2-0, while Peterhead were 3-2 winners at home against Clyde.
Andrew McCarthy, Scott Brown and Russell McLean were on the scoresheet for the hosts, while David Goodwillie scored twice for Clyde, the first from the penalty spot.