The Broncos (3-1) have won three straight since losing its opener while Louisiana-Lafayette (1-3) has dropped its last three.
Ajayi, who amassed 280 all-purpose yards in Boise State's first home game, rolled up 187 total yards. He added five catches for 37 yards.
Louisiana-Lafayette entered the game averaging more than 200 rushing yards per game. However, the Ragin' Cajuns mustered just 67 yards on 23 carries, the lowest total since Arkansas State held them to 66 yards on Nov. 12, 2011.
Through the air was equally daunting for Louisiana-Lafayette. Terrance Broadway, who finished with 20-of-38 passing for 160 yards with one interception, remained under duress most of the game from Boise State's pass rush.
Boise State had little problems against Louisiana-Lafayette's defense. The Broncos took their opening drive 70 yards, 45 of which was gained on the ground by Ajayi, including a 2-yard touchdown run to take a 7-0 lead.
After holding the Ragin' Cajuns without a first down, the Broncos marched 64 yards in four plays on its ensuing possession, capped by another 2-yard touchdown run by Ajayi. Dan Goodale's extra point pushed Boise State's lead to 14-0 with 6:21 remaining in the first quarter.
The Ragin' Cajuns responded with their best drive of the first half, a 12-play, 70-yard drive that included two fourth downs on which Louisiana-Lafayette attempted to kick.
On the first fourth down, Boise State roughed punter Daniel Cadona, giving the Ragin' Cajuns a first down. Six plays later on fourth down from the Boise State 21, Stover Hunter lined up to attempt a 38-yard field goal. However, the snap sailed over his head, but he scrambled to pick it up and completed a 14-yard pass for a first down to tight end Evan Tatford.
The drive finally ended when it stalled at the 5 and Stover booted a 22-yard field goal to cut Boise State's lead to 14-3 with 2:01 left in the opening quarter.
Ajayi tacked on a 16-yard scoring run to give Boise State a 21-3 halftime lead.