Brown made an open-field tackle after Marcus caught Johnny McCrary's pass on the conversion attempt. Vanderbilt had cut the lead to 14-12 when McCrary threw a 2-yard touchdown pass to Trent Sherfield on fourth-and-goal.
Vanderbilt recovered the ensuing onside kick but touched the ball before it traveled the necessary 10 yards.
Leon Allen had a 4-yard touchdown run and Tyler Higbee caught a 9-yard touchdown pass for Western Kentucky. Higbee set up Allen's score with a 65-yard reception.
Tommy Openshaw kicked field goals of 49 and 26-yards for Vanderbilt.
Vanderbilt had three scoreless trips inside Western Kentucky's 10-yard line. McCrary had two passes intercepted in the end zone, and Openshaw missed a 28-yard field goal after a low snap.
