PROVO — After opening Tanner Mangum's collegiate career with a Hail Mary pass to beat Nebraska on the final play of the game, BYU football needed something pretty spectacular for an encore.

They got it.

Mangum scored the winning touchdown on a 35-yard pass to a wide-open Mitch Juergens with 45 seconds left, and Kai Nacua returned his third interception of the night 50 yards for the game-icing touchdown to help BYU upset No. 20 Boise State, 35-24 on Saturday night at LaVell Edwards Stadium.

Much of the offensive performance was inconsistent through the night. But a win over a top-25 team will earn you plenty of good grades on a home opener in Provo.

Offense: B+

It took Tanner Mangum exactly three plays to do what he did to finish off his first college game at Nebraska: Mangum found Mitch Juergens for an 84-yard touchdown pass on just the third play of the game.

Juergens topped the 100-yard receiving mark in the second quarter, grabbing his third haul for 137 yards to go along with the opening touchdown. He finished with 172 yards and two touchdowns on four catches in his first home game since earning a scholarship two weeks ago.

The Cougars struggled to find consistency in the run game, though, piling up just five net yards on nine carries in the opening quarter and finishing the half with 14 yards on 19 carries. Adam Hine came on in the second half, though, leading his team with 93 yards on 19 carries, including a 21-yard TD run with 4:32 left in the third quarter.

After struggling with injuries all summer, Hine has found his form through the first two games of the season as the Cougars' No. 1 running back — and they've needed it.

"One of the main differences in this game was Adam Hine," BYU coach Bronco Mendenhall said. "He helped get some balance back into our game and take some pressure off of Tanner. Our receivers continued to make critical plays when they needed to."

A pass-first offense is fine, but a pass-only offense is only half a game plan — and BYU looked like that for large chunks of the game.

But a 2-0 start pushes the offense up nearly a full letter grade.

"Having an offense that makes big plays gives us a better chance to win," Mangum said. "More than anything, I just do my best to make the right decision. Luckily we have some amazing guys that made some amazing plays, and I tried to make the right decisions."

Defense: B+

After holding Boise to three-and-out on the first drive, Ryan Finley completed his next five passes for 58 yards to set up Jeremy McNichols' game-tying touchdown run from the 3-yard line with 4:13 left in the opening quarter. The Broncos used consistent pressure off tackle to march down the field and tie the game after BYU's hot start, and there was little BYU's linebackers could do to combat it.

Kai Nacua was the star of the show for BYU's defense Saturday night, though, making a play in his first quarter of college football in 2015 by intercepting Finley with 50 seconds left at the 1-yard line. He added another pick in the fourth quarter to set up a 12-yard touchdown drive capped by Mangum's 1-yard sneak across the goal line with 10:22 left to pull the Cougars within three, 24-21, then scored on a 50-yard pick-six to ice the game with 30 seconds left.

"I love Kai," defensive back Michael Wadsworth said of Nacua, who tied a BYU single-game record for most interceptions. "He brings a different energy to the game. I love playing with him. He's a playmaker and you saw that tonight. He's a great guy on and off the field."

BYU started to apply pressure after the first few series, capped by a rim-shaking sack from Harvey Langi after Mangum threw his second pick of the night with 10:54 left in the second quarter. As the linebackers forced obvious passing downs late in the count, the secondary made just enough plays to force a stop.

An overzealous defense almost cost BYU late, when Sione Takitaki drew a tough roughing-the-passer penalty as BYU looked to have Boise State stopped on 3rd-and-16 in the third quarter, and the Broncos used that play to finish off a long touchdown drive with McNichols' second short touchdown run to go up 17-7 with 11:01 to play in the third.

Langi finished with five tackles, two sacks and three tackles for loss, and Michael Wadsworth had a team-best nine tackles and a tackle for loss for BYU.

There were a few miscues, especially in the middle quarters. But in the end, the defense made the plays to get the win — and move to an unbeaten showdown with UCLA at the Rose Bowl next week. And that deserves a decent grade.

Special Teams: C+

Micah Hannemann had a solid debut at punt returner against Nebraska, but the freshman from Lone Peak took a step back Saturday night. Hannemann let his first punt return attempt go for a fair catch inside the 5-yard line, then backed off a ball at the 15 that Boise State down inside the 10 with a bounce. The freshman returned missionary had only one punt return for four years, and Eric Takenaka added one return for three years.

Jonny Linehan also had a few shaky moments, though the junior was also playing in just his second college football game after a lifetime of rugby. The junior rugby star had 310 yards on eight punts for a 38.8 yard-average — which was a step back from his 51-yard average a week ago at Nebraska.

But Linehan redeemed himself a little bit with a punt to the two-yard line when BYU most needed it, trailing 24-14 to start the final quarter.

Coaching: B-

Trying to establish any kind of momentum on the ground, BYU's coaching staff used several runs straight up the middle — but to no avail. By focusing so extensively on the run game early in the second half, the Cougars abandoned what was working early — namely, the passing attack of Mangum and his wide receivers.

But if you sit on the egg long enough, it will hatch, and Hine made his coach look good with a shoestring-tackle-avoiding 21-yard run to pull BYU within three points at 17-14 with 4:32 left in the third quarter.

Yet unlike a week ago at Nebraska, when BYU needed a timeout late in the game, the Cougars had one. There were moments of vanilla play-calling and blunders — in other words, even on the coaching staff, this BYU team is not a finished product. But when a big play was needed, the players were in the right spots to make one.

Overall: B

Whether by skill, luck or a little bit of both, BYU moved to 2-0 on the year and the Tanner Mangum era is currently without a loss. Where will it end in a week's time against the Cougars' first Pac 12 opponent of the year, in the Rose Bowl? That's yet to be seen — but no one can blame BYU for having a little confidence ahead of that game.

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