By ERIC OLSON
AP College Football Writer
LINCOLN, Neb. (AP) - Mike Riley raised clenched fists over his head and looked at the ground, his headset sliding backward.
This surely wasn’t the ending he envisioned for his first game as Nebraska’s coach.
After Riley’s team came back from a 10-point halftime deficit to take the lead, BYU delivered a gut-punch when freshman backup Tanner Mangum heaved a 42-yard touchdown pass to Mitch Mathews with no time left to beat the Cornhuskers 33-28 Saturday.
“Am I supposed to make an opening statement after that?” a stunned Riley asked reporters 10 minutes later.
The Huskers lost their season opener for the first time since 1985, ending the nation’s longest streak.
Tommy Armstrong Jr. passed for 319 yards and three touchdowns, his last one going 9 yards to Trey Foster for a 28-24 lead late in the third quarter, and Jordan Westerkamp caught seven balls for 107 yards.
Nebraska looked to have the momentum in the second half. Its defense clamped down, and Armstrong overcame a mid-game lull to get the offense moving again.
The Huskers were still up 28-27 with 7:57 left after Trevor Samson’s 35-yard field goal for BYU. But the Huskers couldn’t put away the Cougars. When Drew Brown missed a 41-yard field goal for Nebraska, the Cougars started their final drive from their own 35. There were 48 seconds to play.
Mangum, who took over early in the fourth quarter for injured star Taysom Hill, faced four-and-3 from the Nebraska 42 when he launched his winning pass against a three-man rush. Safety Nate Geary was behind Mathews as the ball came down, but he couldn’t break up the pass.
Riley, in his 41st year in coaching, said he couldn’t remember ever losing a game the way he did his first one at Nebraska.
“I initially thought he was not in the end zone, but I had a really bad view,” Riley said. “I saw the official raise his hands right away, so I knew.”
Mathews jumped around at midfield as teammates mobbed him after the play stood up to a video review. A half-hour after the game, hundreds of joyous BYU fans still congregated in the south end zone near where Mathews came down with the ball.
“I had to come down with it,” Mathews said. “I had to come down with it for my guys. Sometime you have to do what you have to do, and that’s catch the rock and win the game. I didn’t know I scored right away because I was under a pile of people. Nick Kurtz was laying on me and was screaming.”
The victory came with a heavy price for BYU. Hill sustained a season-ending injury for the second straight year. Coach Bronco Mendenhall said Hill fractured a foot on a 21-yard touchdown run in the first half. He went to the locker room and missed two plays before returning, then left again after getting hit hard on an 8-yard run in the fourth quarter.
Making Mangum’s dramatic play even more remarkable was that he returned from his two-year LDS mission in June. Mangum hadn’t played in an organized football game since 2012. He finished 7 of 11 for 111 yards and is the presumed starter when the Cougars host Boise State next week.
“I’m amazed that Tanner Mangum, just two months off his mission, coming in and being able to help our team win,” Mendenhall said. “I was just proud of the way he was able to lead our team on the big stage, in an historic stadium, finding a way to pull it out.”
This opener was long anticipated in Lincoln. Riley, who spent the last 12 years at Oregon State, was athletic director Shawn Eichorst’s surprise hire last December after Bo Pelini was fired.
Each team was without players who were suspended for disciplinary reasons. Among the five missing Huskers were linebacker Michael Rose-Ivey, cornerback Jonathan Rose and tight end Cethan Carter. Among the suspended BYU players were defensive lineman Tomasi Laulile, free safety Kai Nacua, linebacker Sione Takitaki and wide receiver Trey Dye.