Lamb was 7-of-13 passing for 161 yards and added 62 yards rushing on five carries for Appalachian State (6-4, 5-1 Sun Belt Conference).
Collin Reed's 23-yard touchdown reception gave the Mountaineers their first lead midway through the second quarter and freshman Chandler Staton hit a career-long 53-yard field goal as time in the first half expired to make it 10-3.
On Appalachian State's first play from scrimmage in the second half, Lamb hit Thomas Hennigan for a 51-yard gain to set up a 28-yard field goal by Staton. Georgia Southern (0-9, 0-5) answered with an 11-play, 36-yard drive capped by Tyler Bass' 44-yard field goal to make it 13-6 late in the third quarter.
On Appalachian State's next possession, defensive end Caleb Fuller, on fourth-and-1 from midfield, ran 23 yards on a fake punt and, three plays later, Lamb hit Ike Lewis for a 20-yard touchdown. The Eagles went three-and-out on their ensuing drive and, after Lamb connected with Lewis for a 30-yard gain on fourth-and-6, Daetrich Harrington's 3-yard scoring run capped the scoring with 9:40 to go.
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