Georgia Southern (11-1), the No. 2 seed which is seeking its third straight national title and seventh overall, scored 33 unanswered points in the second half to outlast Florida A&M, 60-35.
Top-seeded Montana (11-1) rallied from a 13-point deficit early in the second half to get past Northwestern State, 28-19. The Grizzlies lost to Georgia Southern, 27-25, in last year's national championship contest.
Six of eight home teams won Saturday, with two of the games coming down to the final minute.
Sam Houston State (10-2) defeated Northern Arizona, 34-31, on Alex St. Peter's 20-yard field goal as time expired.
Lehigh (11-0), the only unbeaten team in the field, rallied to defeat Hofstra, 27-24, in overtime. The Engineers tied it on Luke Ciannello's four-yard touchdown pass to Jermaine Pugh with 19 seconds left in regulation, then won it on Brian Kelley's 24-yard field goal in overtime.
The only teams to lose at home were No. 4 seed Eastern Illinois (9-2) and McNeese State (8-4).
Adam Benge rushed for 177 yards and four touchdowns as Northern Iowa posted a 49-43 victory over Eastern Illinois, while Maine, making just its fourth postseason appearance, posted a 14-10 victory over McNeese State.
No. 3 Furman (10-2), a rival of Georgia Southern in the Southern Conference, was nearly an upset victim, but Al Means scored on a 19-yard run with 3:07 left to give the Paladins a 24-20 victory over Western Kentucky.
Furman had suffered first-round home defeats the last two years.
In the other first-round game, Jimmy Watkins ran for 216 yards and four touchdowns to lead Appalachian State to a 40-27 victory over William & Mary.
Adrian Peterson, the all-time rushing leader in Division I-AA, ran for 153 yards and two touchdowns for Georgia Southern.
The Golden Eagles fell behind, 21-7 in the first quarter and trailed, 28-7, at the half. But Peterson gave Georgia Southern the lead for good, 33-28, on a 45-yard TD run with 8:14 left in the third period.
Peterson has rushed for at least 100 yards in 41 of his 43 career games, including all 13 playoff contests.
The Golden Eagles also catured back-to-back titles in 1985-86 and 1989-90, but never have won three in a row.
Backup Brandon Neill rallied Montana in the second half after starter John Edwards was benched. Edwards completed just three of seven passes and fumbled twice in the first half.
But the Grizzlies got on the board early in the third quarter on a 12-yard run by Yohance Humphery, who collected 174 yards of total offense. Montana took the lead for good, 14-13, on Neill's 11-yard pass to T.J. Oelkers.
The first three rounds will be on campus sites, leading to the national title game on Dec. 21 in Chattanooga, Tenn.