Bennett put in 22 points to go with seven rebounds. Marshall added 16 and eight.
Mike Moser supplied a double-double of 15 points and 12 boards for the Rebels (3-1), who won the third-place game of the Global Sports Classic.
The Cyclones (4-2) were led by Will Clyburn's 21 points and 15 rebounds.
Tyrus McGee (12 points) and Melvin Ejim (10 points, 11 rebounds) also reached double figures for Iowa State.