The game got out of hand early as the Wildcats (2-0) took a 43-15 lead into halftime after dominating the paint and capitalizing on 14 first-half turnovers by the Cardinals.
Donley Minor scored 17 points and Rhon Mitchell 15 for Lamar (0-1).
The Wildcats owned the boards at both ends in the first half, limiting Lamar to five offensive rebounds. The Cardinals had just four second-chance points and were outscored 18-6 in the paint during the first 20 minutes.
Kansas State opened up the game with a 15-0 run as Rodriguez and Spradling each drained 3-pointers. Lamar committed six turnovers in the first eight minutes.