Duke stayed unbeaten through five games and reached the title contest in the Battle 4 Atlantis.
Virginia Commonwealth surprised nationally-ranked Memphis in the opening round of the tournament and trailed Duke at halftime by a single point.
Plumlee made a layup 5 seconds deep in the second half and added a dunk 37 seconds later to get Duke rolling and the Blue Devils wound up going on a 15-4 surge to take control.
The Rams came no closer than six points the rest of the way.
Plumlee led Duke with 17 points and 10 rebounds, Seth Curry had 15 and Rasheed Sulaimon added 12.
The Blue Devils shot only 41 percent from the field and Curry, Duke's outstanding floor leader, made just 3-of-9 attempts.
Juvonte Reddic and Treveon Graham both had 16 points for Virginia Commonwealth (3-2).