It’s a new USC that begins to prepare for Penn State in the Rose Bowl

Now that USC is 9-3 and has secured an improbable Rose Bowl berth, its players are amused to report that their early assessment of the team was pretty much the same as most fans’.

“We were 1-3, me and my boys were like, ‘Man we suck!’ ” receiver JuJu Smith-Schuster said. “Joking around, though.”

USC’s turnaround, from that 1-3 start to an eight-game winning streak and top-10 ranking, stunned most of the country and is rivaled only by that of the Trojans’ Rose Bowl opponent, Penn State, which won nine games in a row and took the Big Ten title.

Back in September, the idea of the Rose Bowl wasn’t so much a distant goal for USC as a delusion. Even as recently as the Trojans’ last game against Notre Dame, Smith-Schuster predicted that they would end up in the Alamo Bowl.

USC’s climb back to prominence had many engines: Coach Clay Helton’s calm, quarterback Sam Darnold’s mastery and a talented defense’s maturation.

But players say a culture shift began in late September, when the season was on the brink. The Trojans had just collapsed late against Utah. Players said they began hearing calls for Helton’s job. A week earlier, rumors spread that offensive lineman E.J. Price, who’d decided to transfer, had punched Helton in the face. The rumor lacked any basis in fact, but to players, its spread reflected a program that seemed to be spiraling out of anyone’s control.

“We didn’t know what was wrong,” safety Chris Hawkins said.

Team leaders called a players-only meeting to air grievances. At that time, a winning record was of greater concern than any bowl game.

Players who were at the meeting said seniors and others in leadership roles tried to keep the team from fracturing. They addressed players who may have considered transferring.

“Some people got called out,” Hawkins said. “But that’s how it went.”

Smith-Schuster said several players grew emotional. He said he cried.

“It just hurt because we worked so hard,” Smith-Schuster said. “I think the biggest thing that was said in there was that no matter what, it was us against the world. And that was it.”

“From then on,” Hawkins said, “we’ve been all gas.”

In the following weeks, USC improved dramatically in almost all measurable areas.

In total offense, USC leaped from 99th in the nation in September to fifth for games played after that month. That represented a jump from 359 yards per game to 524.

In total defense, the Trojans climbed from 69th (395 yards given up a game) to 17th (341).

Darnold compiled the nation’s second-highest total QBR — ESPN’s metric for evaluating a quarterback’s total contribution. His 87.0 rating trailed only Oklahoma’s Baker Mayfield (91.6). Louisville’s Lamar Jackson, who won the Heisman Trophy, finished third at 86.6, just behind Darnold.

Darnold’s presence rejuvenated the languid offense, but his arrival alone didn’t fully explain the turnaround. The transformation of a young, porous defensive line into a mature, aggressive unit saw USC add more than a sack per game to its September average. The rush defense improved by 92 yards per game.

The offense was a mirror image. USC rushed for 95 more yards per game after September — partially because Darnold’s proficiency compelled defenders to back off the run.

USC swept October and won its first game in November against Oregon. But it wasn’t until its upset win at Washington that players began mentioning a possible Pac-12 title or the Rose Bowl.

Helton didn’t say when he began thinking of Pasadena as a plausible bowl destination.

“When we started 0-2 [in the Pac-12], we kind of went into playoff-football mode,” he said. “We understood that to be able to do something special throughout the season we were going to have to go on a run.”

When the regular-season run was over and the Rose Bowl seemed within reach, senior linebacker Michael Hutchings took a moment to marvel. He stood outside USC’s locker room after the win over Notre Dame and smiled.

“Just from where this program has come since I was a freshman, to going to a Rose Bowl as a senior?” he said. “Nobody would’ve expected that.”

zach.helfand@latimes.com

Follow Zach Helfand on Twitter @zhelfand