Lacey finished with 7-of-9 shooting from the field and hit all four of his free throws for the Midshipmen (15-5, 6-1 Patriot League). Will Kelly added 16 points with five rebounds and Shawn Anderson had 12 points with eight rebounds and five assists.
Navy went 16-9 to open the first half but Lehigh surged 16-4 after that to go on top 25-20 with 5:57 to go before the break. A pair of Lacey dunks helped the Midshipmen regain the lead for a 31-30 advantage at halftime.
Early in the second half, Kelly and Anderson combined on an 8-0 run that gave Navy a 39-30 lead with 16:21 to play and Lehigh trailed the rest of the way.
Tim Kempton led the Mountain Hawks (5-13, 3-4) with 16 points and seven rebounds.