Greiner had 12 points and 10 rebounds for the Mountain Hawks (15-5, 5-1), who bounced back from a 78-57 loss to Lafayette on Sunday that snapped their five-game winning streak.
Lehigh trailed 8-1 in the first 4 minutes, then rattled off 14 straight points en route to a 28-18 halftime lead. The Midshipmen could get no closer than eight the rest of the way.
The Mountain Hawks outshot Navy 46.3 percent (25 of 54) to 28.8 percent (19 of 66). Mackey McKnight dished out seven assists for Lehigh.
The Midshipmen (7-15, 1-5), who have lost three straight and nine of their past 10, have averaged 49.6 points in their five most recent losses.
Purdue coach Matt Painter says players haven't used the fifth-year graduate transfer rule for its true intent.
The 2017 recruiting class is short on point guards, with Trevon Duval leading only eight prospects from the ESPN 60 who are still available.
The dust has settled after players made their NBA draft decisions. Which college teams won? Which lost? Well, Villanova is pretty happy. USC, meanwhile, might not be as thrilled.