The Boise State football team’s defense lost five players after last season who are now on NFL rosters, replaced most of them with sophomores and freshmen and has carried the Broncos through the first three games of 2012.

The defense has scored two touchdowns and recovered a fumble on the opponent’s 1-yard line while allowing just 35 points — down from 57 points in the first three games last year.

“They’ve got great swag about them,” Boise State coach Chris Petersen said after the defense fueled a 7-6 defeat of BYU on Thursday night at Bronco Stadium. “They’ll build on this.”

Boise State held BYU to 200 yards and forced five turnovers. Defensive tackle Mike Atkinson scored the Broncos’ only touchdown on a 36-yard interception return and linebacker J.C. Percy batted down a two-point pass with 3:37 left in the game.

It was an inspired effort full of big plays from a defense that has been placed in some difficult situations this season by an underperforming offense.

“We really had a good week of practice on a short week, which was surprising,” Petersen said. “The kids were ready to go. BYU came out and did a few things differently on offense against our defense and they still responded — and they just played great.”

The Broncos started four sophomores and a freshman — defensive ends Demarcus Lawrence and Sam Ukwuachu (the freshman), cornerback Bryan Douglas and safeties Jeremy Ioane and Lee Hightower. Sophomore ends Beau Martin and Tyler Horn and freshman safety Darian Thompson also played.

So far, they don’t look like they’re new at this.

“I’ve got to say it’s coaching,” Percy said. “And then also, the young guys have the will to learn and they go and they latch onto the older guys.”

Said Kwiatkowski: “It’s two-fold. It’s the players buying in and continually getting better. And … we’ve got a really good staff, very knowledgeable coaches. They do a great job communicating with the players on how we want to play and then the players are doing a great job of listening and showing up on (game day) with great attitude and effort and intensity.”

Lawrence, a junior college transfer who arrived in January, was one of the defensive standouts for the third straight game. He finished with four tackles, a sack on the first play of the game, a fumble recovery and the forced fumble at the 1-yard line. He also served as the lead blocker on Atkinson’s touchdown.

“Demarcus is a guy who continually shows up,” Kwiatkowski said.

The old guard had a big night, too.

Percy led the team with 12 tackles. Senior cornerback Jamar Taylor recorded seven tackles, a sack, a forced fumble and an interception. And Atkinson was a disruptive force all night, clogging running lanes and pressuring the quarterback.

“We had a lot of guys who played at a high level,” Kwiatkowski said. “… Everybody really played fast and they played with that chip.”

BYU’s only points came on an 11-play, 95-yard touchdown drive in the fourth quarter, led by backup quarterback Taysom Hill.

“We had opportunities to get out of that drive,” Kwiatkowski said. “It came down to (Hill) making plays.”

But the defense didn’t buckle after Hill scored on a 4-yard run. Hill rolled out to his right on the two-point play and had an open receiver in the back of the end zone, but Percy — who was not defending that receiver but was running across the end zone to track Hill — dove and knocked down the pass.

“I can’t say enough good things (about the defense),” Petersen said. “It was spectacular.”

THREE CORNERS, TWO SPOTS

Douglas has replaced senior Jerrell Gavins as the starting cornerback opposite Taylor. Gavins rotates into that spot and also plays as a third cornerback in certain situations.

Gavins, a returning starter, has been listed as the starter on the depth chart but Douglas has started each game. Gavins is coming off a serious knee injury from last season and was limited in fall camp.

“Jerrell was hurt and Bryan stepped his game up,” Kwiatkowski said. “We’ve got three corners who can start … but only two can start.”

CROWD RESPONDS

Petersen asked the crowd to make life difficult for BYU’s offense Thursday, and the fans delivered. BYU used all of its timeouts before the closing minutes of the game, when the Cougars might have been able to force a punt.

“There were two entities out there that I was so impressed with and so excited about,” Petersen said. “One was our defense and two was the crowd and Bronco Nation. They answered, and I guarantee that helped us win. I know when people are used to seeing a lot of fireworks on offense, it’s easy to get excited, and they weren’t seeing that on offense and they still came through.”

DRIVE KILLERS

The Broncos have scored three touchdowns and kicked three field goals on 12 red-zone possessions. The goal is about 70 percent touchdowns — and the Broncos are at 25 percent. They converted 74.3 percent last year.

The Broncos also are 17-of-46 combined on third and fourth downs this season — a 37 percent conversion rate.

“Third down is money down,” quarterback Joe Southwick said. “You’ve got to be able to on third down make some things happen. … I can do some better things. Third down, past 3 (yards), is usually in my hands. I need to do a better job, no doubt.”

Chadd Cripe: 377-6398, Twitter: @IDS_BroncoBeat