James Hulbin sealed the win with a late steal for the second-seeded Demons (23-8), who earned their third overall trip to the national event and first since 2006.
DeQuan Hicks also reached double figures for the Demons with 13 points.
The top-seeded Lumberjacks (27-4) were led by Desmond Haymon's 23 points.
Taylor Smith supplied a double-double of 16 points and 14 rebounds for Stephen F. Austin.
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