LSU (5-0) found itself trailing 9-7 late in the first half, but then rattled off the next 24 points to put the contest away.
Mettenberger, who hooked up with Odell Beckham on both of his scoring strikes, completed 15-of-26 passes for 238 yards.
Beckham finished with five catches for 128 yards and Russell Shepard picked up 78 rushing yards for a touchdown for LSU.
Towson (2-2) was led by Grant Enders, who passed for 103 yards and a touchdown and also rushed for 86 yards.
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