Everyone says the game of football is a game of momentum.

Riley Nelson proved that is a scientific fact.

Nelson pulled off one of the biggest change-of-momentum performances ever witnessed in LaVell Edwards Stadium Friday night.

All he did was lead BYU's struggling offense to a pair of fourth-quarter touchdowns and lift BYU to an emotional 27-24 comeback win over snake-bit Utah State. Nelson had career highs in TD passes and yards in just over 20 minutes of clock time.

Nelson took BYU on a 96-yard touchdown drive in the final 2:46 with the Cougars behind 24-21 to electrify Cougar TD-starved partisans perched in the stands. Nelson almost single-handedly put BYU's offense on his back and willed the Cougars to victory.

No kidding. It was movie stuff.

On The Drive, Nelson completed four of five passes for 66 yards and ran for 32 more.

On that winning drive, USU almost caught Nelson for a safety on one end of the field with just under three minutes to play in the game. Yet, Nelson celebrated the winning touchdown at the other end of the field with 11 seconds left on the clock.

How does that happen? Well, it did.

Nelson replaced sophomore Jake Heaps late in the third quarter and immediately led BYU to four scoring opportunities. Two of them backfired on a missed Justin Sorensen field goal and a fumble by JJ Di Luigi.

But despite those kinds of setbacks, all too common by the BYU offense this season, Nelson's touchdown passes of 24 and 13 yards to Cody Hoffman and Marcus Mathews put the hammer on the Aggies.

It was straight from Siegfried and Roy, a circus act.

Nelson's impact was clear and obvious.

Offensive coordinator Brandon Doman approached head coach Bronco Mendenhall in the third quarter and told him he'd like to insert Nelson to "add an element of the run" to the attack and hopefully get the offense some energy.

Where Heaps had been insecure and unsure, Riley oozed macho.

Where Heaps didn't appear hungry or play with a sense of urgency this season, Nelson was starved to make a play.

Where Heaps had shown a casual approach to third-down conversions, Riley made it a matter of life and death.

Where Heaps was quick to get rid of the ball, Riley examined the defense and attacked with his arm or legs, his strength as a quarterback.

Suddenly, BYU's offense, slumbering through the toughest part of the season, sensed a kill.

Receivers started diving for balls. Blockers started hitting harder. BYU runners found new spunk to their gait.

Momentum changed like a light switch. A replay even overturned a field call by officials on one of his passes.

Even his winning touchdown pass to Mathews was a pass tipped by an Aggie defender, intended for Di Luigi.

How does that happen?

Well, it does, when the night belongs to Nelson.

"He's gritty and toughy," said linebacker Brandon Ogletree. "He's had a tough road and stayed with it. Inspiring."

Nelson stunned the Aggie defense with what Mendenhall called "unconventional" plays. Nelson took off and ran out of the shotgun on pure QB draw plays. Even when the Aggies loaded the line of scrimmage with eight defenders, Nelson found a way to squeeze through for play after play.

Nelson's flutter passes found their targets time and time again. He finished the game completing an impressive 10 of 14 passes for 144 yards, his longest a scrambling, running, reloading toss to McKay Jacobson of 40 yards.

Nelson did to Utah State what Texas did to BYU's defense. Like the Cougar defenders in Austin two weeks ago, the change-up in quarterback play caught the Aggies unprepared and trying to adjust on the fly late in a close game.

They could not do it after holding momentum for almost three quarters of the game, including the first call from a scrimmage, an 80-yard touchdown run by Robert Turbin.

"You have to cover so much longer," said Mendenhall of a defense that has the threat of a running quarterback, something he'd prepared for with USU starter Chuckie Keeton.

USU never game-planned for an extended dose of Nelson.

Nelson's energy was so obvious in the game it breathed new life into BYU's defense late in the game. Cougar defenders held USU to only a field goal in the final 20 minutes of the game.

"I wouldn't put anything past Riley," said Mendenhall. "I wouldn't say that to take anything away from Jake, but I'm very proud of him."

To say the Aggies were stunned with Riley is an understatement.

The Aggie defensive weakness was pass defense and they lost their starting safety McCade Brady on a controversial ejection early in the first quarter.

But BYU couldn't take advantage of it until Nelson, and he did so with his legs first.

Nelson finished the game with a whopping 204.97 pass efficiency rating. He passed for 144 yards compared to Heaps' 107 with 11 fewer attempts and just one fewer completion.

His ability to run a hurry-up offense with the run also threw a change-up for the Aggies.

"We did it with a wrinkle, the run," said Nelson. "We ran our stuff and guys made plays," said Nelson.

"This game showed who we are," said Nelson.

A momentum changer, he certainly is.

That was definitely Mr. Nelson under Friday night's lights.