The Buffaloes (1-5, 1-2) fell to 2-1 at home in Thursday night ESPN games. They beat Stanford in 1990 and West Virginia in 2008 and trailed 20-17 in this one at the break after scoring 10 points in the final 24 seconds of the first half.
"We have a lot of momentum," Buffs coach Jon Embree said at halftime.
Not for long.
Ross took the kickoff a yard deep in his end zone and darted down the right sideline untouched, reaching the other end zone 11 seconds later to make it 27-17.
That jump-started a 31-0 second-half onslaught by the Sun Devils.
Grice's third touchdown, from 20 yards out, made it 34-17 heading into the fourth quarter.
Just before halftime, Colorado's Jordan Webb hit tight end Nick Kasa over the middle for a 23-yard TD, and Jamal Miles fumbled the ensuing kickoff at his 17. K.T. Tu'umalo recovered for Colorado and after two shots into the end zone came up empty, Will Oliver nailed a 36-yard field goal as the first half expired.
The Sun Devils struck first when Kelly threw a screen pass to Grice, who weaved his way for a 37-yard score in the first quarter. Nate Bonsu blocked Joe Mora's extra point, leaving Arizona State with a 6-0 lead.
"That's just one less point that they have," Bonsu said at halftime. "And that's huge because that could be the difference in the game."
The Buffs couldn't keep up with the up-tempo Sun Devils to make that miss matter, however.
Alex Garoutte replaced Mora after the Sun Devils' next score and kicked his 25th PAT in 25 tries, giving Arizona State a 13-7 lead following Kelly's 34-yard strike to running back D.J. Foster.
Will Sutton's 8-yard sack of Webb helped the Sun Devils force a three-and-out and the Arizona State offense needed just three plays and 61 seconds to stretch its lead to 20-7.