Unranked Elon even held the lead against No. 1 Duke late in the first half, at 21-20, behind big early production from Sebastian Koch, who finished with 14 points and nine rebounds.
But after Duke guard Quinn Cook's three with one second left in the first half gave the Blue Devils an eight-point lead, the Phoenix never really got back into the game.
Plumlee and Tyler Thornton, who scored all six of his points off the bench in the second half, took over from there, as Duke extended the lead to 11 points within the second half's first five minutes and never looked back. Blue Devils forward Ryan Kelly finished with 14 points to help Duke stay undefeated.