Fatigue set in. Faith, always fragile, began to falter. USC’s revamped defense had held up well for the most part. The new starting quarterback looked confident for the most part. But USC had less and less control of the season’s opening game since halftime. One drive was ruined by a botched trick play. Another was ruined by a fourth-down punt.

Still, Miller Moss was undeterred. More than nine months had passed since the quarterback’s memorable Holiday Bowl debut, long enough to seriously wonder if his six-point performance was just a mirage of bowl season. But Moss was undeterred, even when LSU defenders rushed him on third down in the fourth quarter and he threw an improbable pass into the corner of the end zone where Ja’Kobi Lane had his arms outstretched for a touchdown.

Moss pumped his fists in celebration and roared to the highest ranks of Allegiant Stadium. His spirited performance secured a 27-20 season-opening victory against an SEC opponent.

After that stunning score, USC still needed some help as the defense was deep in its own zone and Moss maneuvered the Trojans down the field to set up a game-winning touchdown run by Woody Marks.

After an offseason filled with uncertainty and unanswered questions, Moss and the Trojans delivered a resounding victory over the 13th-ranked Tigers, marking the first time coach Lincoln Riley beat a team ranked higher than himself in his three seasons at USC.

He had new defensive coordinator D’Anton Lynn to thank for that, as USC’s defense held the opposing offense to just two points for the first time since last September. The Trojans still gave up 421 yards, but LSU averaged just 6.6 yards per play, a marked improvement from last season. USC’s tackling was also much better, and they made key stops with their backs against the wall.

Moss took advantage of these stops and completed 27 of 36 passes for 378 yards and one touchdown.

USC wide receiver Zachariah Branch evades a tackle attempt by LSU linebacker Harold Perkins Jr. after catching a ball in the first half.

(Robert Gauthier/Los Angeles Times)

LSU initially had no trouble moving the ball against USC’s newly formed defense, as Garrett Nussmeier got rid of the ball quickly and neutralized USC’s pass rush with a barrage of short and intermediate passes. He completed 20 of 24 passes in the first half for 191 yards and directed four drives with more than eight plays each, including a 13-play opening drive that put USC under pressure until the Trojans made a crucial stop.

Before a fourth down attempt by LSU inside the 3-yard line, USC launched a perfectly timed inside blitz from linebacker Mason Cobb, forcing Nussmeier to make one of the few missed throws.

USC’s offense took a little longer to get going after barely touching the ball for three minutes in the first quarter.

But while LSU played conservatively with its new quarterback, Moss let loose early and often. In the first half alone, he threw six passes of 17 yards or more, with the most spectacular pass being thrown into a crowd of USC defenders, only for wideout Kyron Hudson to leap up and intercept the ball one-handed.

Hudson’s spectacular catch proved to be the catalyst USC needed, as Marks scored a touchdown two plays later.

That was the only time the Trojans reached the end zone in the first half, although they drove deep into LSU territory twice more. One drive, sparked by an electrifying return from Zachariah Branch, stalled at the 5-yard line and ended in a field goal. Another drive in the final seconds of the first half was less fortunate.

With a minute left, USC wasted valuable time before going into overdrive and advancing to the LSU 12-yard line. Instead of throwing a quick shot or two into the end zone, Riley decided to play it safe, run the ball, and kick the easy field goal to end the second quarter.

USC wide receiver Makai Lemon, right, is tackled by LSU safety Sage Ryan (3) in the first half on Sunday.

(Robert Gauthier/Los Angeles Times)

But Michael Lantz, the Trojans’ new kicker, missed the 29-yard attempt.

As the game slowed in the second half with both defenses applying pressure, USC’s missed opportunity was palpable. Midway through the third quarter, LSU began to impose its will on the ground, just as Tigers left tackle Will Campbell had promised earlier in the week. Running back John Emery Jr. made one long run, then another two plays later.

Only when safety Kamari Ramsey fell in coverage on third down was Nussmeier able to find wide receiver Aaron Anderson for a touchdown and thus establish a lead that, however, was not to last.