Rennie had 126 yards on the ground, including TD runs of 20 and 9 yards for the Panthers (1-1). His first TD broke a 13-13 tie and put Northern Iowa ahead for good with 7:50 remaining in the third quarter. The Northern Iowa quarterback was also 9 for 25 passing for 151 yards.
Johnson added 87 yards rushing with a pair of 1-yard TD runs.
Stephen F. Austin (1-1) outgained Northern Iowa 407-362, but committed four turnovers and three times had to settle for field goals from Jordan Wiggs.
Brady Attaway completed 23 of 35 passes for 281 yards and a touchdown for the Lumberjacks, but was intercepted three times. Corde Roberson had seven catches for 115 yards.