Boise State crowded the tackle box on the first play of Saturday night's game with nine defenders. No. 19 San Diego State couldn't have cared less. It was going to run its best player, tailback Rashaad Penny, right at the teeth of the defense.

One team sent a message on that play which reverberated throughout three hours and 13 minutes of Mountain West Conference football. It wasn't the ranked, undefeated team playing for a shot at a New Year's Day bowl bid.

Instead, the Broncos dropped Penny for a one-yard loss, the first of 12 plays on which they knocked San Diego State backwards. Boise State dominated the Aztecs' offensive line all night long en route to a 31-14 verdict at SDCCU Stadium in San Diego.

Penny managed a season-low 53 yards on 21 carries for San Diego State, which picked up only 83 yards on 39 rushes.

"We had guys in the box, and that's what you have to do to play a team like that, and we tackled," Broncos coach Bryan Harsin said. "I thought we created penetration, which hasn't happened to San Diego State, and the guys on the edge tackled well. They played fast and physical, and that's what happens when you play well."

In winning its third straight game, Boise State (4-2, 2-0) overran the Aztecs at the point of attack. It gave up only 80 yards and six first downs in the first half, forcing San Diego State (6-1, 2-1) into passing situations and hassling quarterback Christian Chapman.

Without the running game to give him one-on-one matchups on play-action throws, Chapman hit just 12 of 27 passes for 240 yards. He was sacked four times, hit at least 10 other times and rarely had a clean pocket.

"I hate losing more than I like winning. This was a big loss," Chapman said. "We had a goal. We were trying to go undefeated. That's out the window now. They beat us fair and square, man. You've got to tip your hats off to them. They were more physical than us. They just beat us at the line of scrimmage. They were just a better team tonight. But the goal still remains the same, trying to win a championship out here.

Chapman, known for his clean play, mixed in a huge mistake late in the first quarter. Trying to avoid a sack, Chapman tossed the ball backwards. Kekaula Kaniho picked it up and rumbled 34 yards for a touchdown and a 14-0 lead with 4:20 on the clock.

"The quarterback puts himself in a bad position, and (Kaniho) knows what to do with it," Harsin said. "Being opportunistic, sometimes, is what it comes down to."

That score came less than two minutes after Avery Williams returned a punt 53 yards, traversing the field from left to right after appearing to be hemmed in near the sideline, to initiate scoring.

The Broncos' offense joined the fray late in the second quarter, driving 77 yards for a touchdown after being held to one first down for about a quarter and a half. Brett Rypien finished the drive with a 3-yard scoring strike to Jake Roh, making it 21-0 at the half.

The Aztecs did manage one burst of competence in the second half. Chapman found Fred Trevillion in stride for an 89-yard touchdown pass with 4:15 left in the third quarter.

After Haden Hoggarth converted a 19-yard field goal on the fourth quarter's second play for Boise State, San Diego State ripped off an 84-yard scoring drive. Penny capped it with an 11-yard run at the 10:06 mark to pull the Aztecs within 24-14.

However, the Broncos iced it with a punishing 70-yard drive on which all nine plays were runs. Alex Mattison pounded into the end zone from the 4 with 4:52 left, finishing any longshot comeback hopes San Diego State harbored.

"Everyone had the correct mindset going into the week that we were just going to pound the rock," Roh said.

Mattison collected 128 yards on 23 carries, while Rypien hit 11 of 19 passes for a modest 72 yards as Boise State was outgained 323-311.

But with their defense and special teams setting an early tone, the Broncos were in control. And the Aztecs' hopes of a perfect season were ruined.

"I thought it was very obvious they were the most physical football team out there tonight," San Diego State coach Rocky Long said.

NOTES: San Diego State is the FBS leader in turnover margin dating back to the start of the 2015 season at plus-43. Alabama ranked second at plus-32. ... Boise State owns a 119-15 conference record since 2000, the best among all FBS schools. ... Aztecs RB Rashaad Penny went over 1,000 yards with a 21-yard run in the first quarter, and is the first SDSU player to rush for more than 100 yards in the season's first six games since Marshall Faulk (1992).