Riddle went 18 for 33 for 230 yards, including a 7-yard touchdown pass to Terrell Hudgins and a 55-yarder to Sean Jeffcoat. Hudgins caught six passes for 65 yards.
The win gave the Phoenix back-to-back wins over the Bulldogs for the first time.
The Phoenix (5-1, 3-0 Southern Conference) piled up 543 yards total offense. Jamal Shuman rushed for 167 yards, the third time this season he has gained at least 100 yards rushing.
Karlos Sullivan returned an interception 14 yards for a touchdown and Adam Shreiner kicked three field goals for the Phoenix.
The Citadel managed only 120 yards total offense.
Bart Blanchard was 14 of 25 for 102 yards with two interceptions. He threw a 5-yard touchdown pass to Kevin Hardy in the fourth quarter.
CHATTANOOGA 14, SANFORD 7
In Birmingham, Ala., B.J. Coleman threw for 249 yards in Chattanooga's win.
Coleman, who was 18 of 31, scored the first touchdown for the Mocs (4-1, 2-1) on a 1-yard run with 6:31 left in the first quarter.
Chris Pitchford had five passes for 135 yards for Chattanooga, which is 4-1 for the first time since 1997. The Mocs also opened the season 2-0 on the road for the first time since 1980.
Chris Awuah, who finished with 40 yards rushing, scored on a 1-yard run with 9:40 left in the first half for a 14-0 Chattanooga lead.
Dustin Taliaferro put the Bulldogs (3-3, 1-2) on the scoreboard with a 1-yard run with 9:52 left to play.
Samford was led by Taliaferro, who was 25 of 31 with 165 yards and one interception.
APPALACHIAN STATE 55,
NORTH CAROLINA CENTRAL 21
In Boone, N.C., Devon Moore rushed for 124 yards and Appalachian State dominated in the running game to blow out North Carolina Central.
The Mountaineers (3-2) had 407 yards on the ground and six rushing touchdowns.
Appalachian State trailed 14-7 in the first quarter but responded with 27 points in a row. Armanti Edwards put the Mountaineers ahead 34-14 on a 7-yard run with 3:15 left in the third quarter.
Edwards finished with 97 yards and two touchdowns on 10 carries, and was 17 of 29 for 237 yards and a touchdown passing.
After gaining the early lead, the Eagles (0-6) scored just once in the second half, on a 44-yard pass to Andrew Johnson from Michael Johnson early in the fourth quarter.
Michael Johnson was 16 of 23 for 186 yards and two touchdowns for North Carolina Central.