Mo Alie-Cox hit 8 of 11 from the field to score 18 points and grabbed 11 rebounds for VCU (16-5, 8-0 Atlantic 10).
Johnson had 15 points and Cox 12 in the first half when the Rams made 17 of 32 shots to build at 38-28 lead. The Wildcats had rallied from a 22-7 deficit less than eight minutes into the game.
Jack Gibbs scored 25 of his 37 points in the second half for Davidson (12-7, 4-4), which had its 15-game home winning streak snapped, but Lewis had 17 of his points to protect the VCU cushion. The Rams also had a 23-9 rebounding advantage after halftime.
Davidson got within two on a Gibbs 3 with 6:51 left but the Rams scored the next nine to lead 66-55 with 4:30 left.