The Flames (7-15, 3-5 Big South Conference) led 47-45 when they launched a 16-4 run, capped by Marshall's third trey in the spurt with 10:50 remaining. Liberty made 6 of 8 3-pointers in the second half.
Although ranked last in the Big South in field-goal percentage (41.4), the Flames shot 57.4 percent (27 of 47), including 66.7 percent after the break (16 of 24). The Camels (10-12, 5-3), the league leaders at 45.4 percent, shot 40.3 percent (25 of 62).
Speaks, who posted a career high, scored 17 points in the first half, making 4 of 5 field goals and 8 of 8 free throws. He has scored in double figures in 11 straight games.
Trey Freeman led Campbell with 17 points.
Mike Krzyzewski says he has good reason to be excited for next season thanks to a combination of Duke's incoming freshmen and a core of experienced upperclassmen.
Georgia guard Juwan Parker has been awarded a medical redshirt, leaving him with two years of eligibility, after missing the 2015-16 season with a partially torn Achilles tendon.
Forward Trevon Bluiett has withdrawn from consideration from the NBA draft and will return to Xavier for his junior season.