The Dukes won their fifth straight game and earned a meeting in the East Region with top-seeded Indiana on Friday.
James Madison won the Colonial Athletic Association Tournament as the No. 3 seed to get into the NCAA event and finally pulled away in the game's final stages while improving to 20-14.
LIU-Brooklyn overcame a 12-point deficit in the first half to take a one-point lead early in the second period and still trailed by only five with 4:53 to play.
That is when James Madison put together its 8-0 surge with the first four points coming from Nation.
A.J. Davis led the Dukes with 20 points, Charles Cooke had 15 and Nation finished with 14.
James Madison is making its first NCAA appearance in 19 years and this was its first victory in the tournament since 1983, when the Dukes downed West Virginia in the first round before losing to North Carolina.
LIU-Brooklyn (20-13), winner of the Northeast Conference Tournament, made its second NCAA trip in as many years. The Blackbirds last won a game in the event 40 years ago. They were paced by 20 points and 10 rebounds from Jamal Olaseware.