Sampson, who entered the game averaging 6.7 points and seven rebounds, also added 17 points. Kemp, who scored nine of his points from the free-throw line, grabbed 11 rebounds for the Pirates (4-0).
Appalachian State (1-3) scored the game's first four points and led 6-2 after Nathan Healy hit a jumper. But East Carolina used a 14-4 run to go ahead 16-10 with 14:29 left in the first half.
Appalachian State cut the deficit to 23-22 later in the half but would not get any closer as East Carolina took a 38-33 advantage into halftime and never led by less than four in the second half.
Jay Canty had 25 points and Healy added 24 points and 10 rebounds for Appalachian State.
Northwestern has never made the NCAA tournament, but the Wildcats' upward trajectory suggests 2016-17 could finally be the season it happens.
Dillon Brooks, who led Oregon with 16.7 points per game last season, will opt out of the NBA draft process and return to the Ducks, a source told ESPN.
Mississippi State freshman guard Malik Newman will withdraw from the NBA draft, but sources told ESPN he might explore other opportunities besides returning to Mississippi State.