We saw an offense come alive that had been, to quote Miracle Max, mostly dead not just for the first three quarters against the Aggies, but for the better part of five games.
Mendenhall was relieved by the victory, but is now vexed by it.
He has to pick a quarterback: Is it Heaps or is it Nelson?
It has to be one or the other.
Those who say the quarterback position should be the same as any other whoever plays the best, in this case, whoever moves the offense in any given moment or any series of moments, should be the starter.
That's what you do at linebacker or right tackle or left defensive end. It's not what you do at quarterback. You replace sergeants and lieutenants, as though they were spark plugs and oil filters, but you don't sack your general, you don't switch out supreme commanders like you rotate your Michelins, depending on momentary results.
It's not an easy decision for Mendenhall, but not deciding is the worst plan he could follow, just like it was a year ago.
For whatever reasons, Heaps right now is lost in a fog. He has the better arm, the better upside, the better form. But he has backed up in his progression. Nearly everyone, myself included, mistakenly thought this season was his time to step into the role of a confident passer, to take control of an offense that seemed perfectly suited for him.
But he's played scared, he's played soft, as though he doesn't want to get hit, he's played like he's got something else on his mind, distracted by some sort of unrelated personal problem, and he's scattered the ball around like buckshot out of a sawed-off shotgun.
Nearly as bad, he's seemed detached from reality. Before the season began, he talked about winning a national championship. Newsflash: The Cougars wouldn't win a national title with Tom Brady under center. After poor performances and big losses, he blew mostly sunshine. Nonchalant arrogance emanated from him that was a sloppy veneer for missing authentic swagger.
And worst of all, his team quit following him.
Nelson's insertion the other night invigorated the entire outfit, creating enthusiasm that not only endorsed the backup, it swatted the starter upside the head. Every compliment spoken about Nelson such as Brandon Ogletree's: "You saw the way the team rallied around him" was an indictment of the other guy.
Point is, the team has not rallied, does not rally around Heaps. For weeks, players in the program have whispered complaints about the sophomore's immaturity.
When Nelson entered, the blocking was better, the effort was better, the results were better. Does that make him a better quarterback?
That's the irony. He is not.
Send Heaps and Nelson to a college combine, assign them anonymous jerseys and random numbers, and have recruiters and scouts judge their overall abilities, and 19 of 20 would nod in favor of Heaps.
Nelson thrived in chaos against Utah State. Give good teams a chance to prepare for him and the Cougar offense would continue to struggle. Fortunately for BYU, there aren't many good teams left on its schedule.
Heaps essentially needs to get real, grow up, gut up, and earn his teammates' respect. That could still happen this season, if he did some soul-searching and got a second chance from the coaches.
In addition, those coaches, including Mendenhall and Brandon Doman, must take responsibility, too, for not properly preparing Heaps, not grasping what was happening within the team, and not following whatever course would have averted the offensive struggles.
There's major excitement among Cougars right now about Nelson's performance in that last possession on Friday. There are those who have even invoked the name of Steve Young in singing Nelson's praises.
Nelson has hung in there, and worked hard over a long stretch that must have been difficult for him after what happened last season. He can't throw much, but Mendenhall loves the dude, calling him a quality kid and a great leader.
Here's the thing, though: If he's the answer for BYU at quarterback, something has gone horribly wrong, and that's not all Jake Heaps' fault.
Recovering from this mess is more complicated than just naming Nelson the starter now on account of what went down against the Aggies.
Still, the worst thing Mendenhall can do is waffle. He must show leadership and be decisive and make a decision that makes real sense. On Monday, he said a starter would not yet be named. That might work for confusing San Jose State, but if he confuses his players, as well, that's trouble. He also said he would prefer to avoid a repeat of last year's mistake.
Based on talent, Heaps should be the guy, and Nelson a situational Plan B, but only in very limited doses. Mendenhall somehow has to channel Dr. Freud and rearrange the mess in Heaps' head. That's the best solution, it's the only lasting solution, to an offense in huge need of repair.
GORDON MONSON hosts "The Gordon Monson Show" weekdays from 2-6 p.m. on 97.5 FM/1280 AM The Zone.