But then an interception of Nelson led to a Ute field goal, followed by an errant shotgun snap that Utah's Moe Lee returned for a touchdown. Those plays helped Utah take a 24-7 lead after three quarters and hold on for the victory.
Nelson tried to pull off an improbable comeback. His bomb to Cody Hoffman moved BYU to the Utah 34-yard line, and then a penalty on Utah after the crowd rushed the field gave BYU a second field-goal attempt that hit the left upright and bounced away.
A few more big road games await Nelson against Boise State on Thursday and Notre Dame and Georgia Tech in October, but this was a missed opportunity for him - and his possible place in BYU's quarterbacking history. In the past 40 years, Nelson and Kevin Feterik are the Cougars' only senior QBs who have lost to the Utes.
This was Nelson's first competition at Rice-Eccles Stadium since leading Logan High School to the 2005 Class 3A championship.
Summarizing his journey to this point in advance of Saturday's game, Nelson said, "I'm hoping that the body of work, the culmination of those seven years, make it so that walking out on the field, I can be nice and calm and poised."
That was before he knew how much would go wrong - and right - for him and the Cougars in this game.
His 10-yard touchdown pass to Cody Hoffman enabled the Cougars to tie the game (7-7) late in the second quarter. Actually, Nelson made just as important of a play on the previous drive, when he somehow recovered his own fumble after being sacked.
The Cougars drove to the Utah 28-yard line before being pushed back. Yet thanks to Nelson's recovery at the 38, Riley Stephenson was able to punt the ball to the 1-yard line. After the Cougar defense forced a three-and-out, BYU took over at the Ute 33 and moved efficiently to the end zone.
That preservation of field position made Nelson's recovery so critical.
It was shaping up as that kind of fortuitous night for Nelson. On BYU's very first play, the shotgun snap went past him and rolled deep into the end zone, before Nelson could corral the ball. But because Utah's Joe Kruger grabbed Nelson's facemask, BYU avoided a safety.
On the first possession of the second half, Nelson got another break. His fumble, recovered by Utah, was overturned by replay (and ruled an incompletion). Basically the same thing happened later in the third quarter.
In between, the Utes had finally held onto one of Nelson's passes. Utah turned Ryan Lacy's interception into a field goal for a brief 10-7 edge. And then the Utes managed to corral a Cougar fumble. Another shotgun snap went past an unsuspecting Nelson and was eventually grabbed by Ute cornerback Moe Lee, who sprinted 47 yards for a touchdown.