Although a fourth-quarter flurry erased the Trojans' struggles on the scoreboard, they left with respect for the Broncos and determination to get better.
Ronald Jones II ran 37 yards for the tiebreaking touchdown with 6:57 to play Saturday, and No. 4 USC rallied from a second-half deficit for a 49-31 victory in both schools' opener.
"It's just stuff that we have to go through," said Darnold, who failed to throw a touchdown pass for the first time during USC's 10-game winning streak. "You're going to have little mistakes. You're going to have setbacks, but we have to learn from them and get better."
Jones rushed for 159 yards and three scores, while freshman Stephen Carr added 69 yards rushing and two TDs in an auspicious debut for the Trojans, who scored 28 points in the fourth quarter.
Marvell Tell returned an interception 37 yards for a TD with 3:13 to play as USC won its 10th consecutive game despite major trouble from the defending MAC champion Broncos on a brutally hot day at the Coliseum.
"I am happy to have that type of experience," USC coach Clay Helton said. "I'm happy it wasn't easy, and was a hard-fought game. We know that there's a lot of progress that needs to be made, and very quickly."
Darnold passed for 289 yards and rushed for a score, but the junior had thrown at least two touchdown passes in each of the Trojans' previous nine games, including his record-setting performance in last season's Rose Bowl . Deontay Burnett caught seven passes for 142 yards.
Jon Wassink passed for 67 yards, caught a touchdown pass and rushed for another score in coach Tim Lester's debut for his alma mater. Even after losing coach P.J. Fleck, quarterback Zach Terrell and star receiver Corey Davis, the Broncos' 15 returning starters came back strong after winning 13 games and reaching the Cotton Bowl.
"Our guys came to play," Broncos tailback Jamauri Bogan said. "We knew that we would show up. We knew that the country would expect us to fold. I really feel like we laid it on the line, and we're ready for next week."
After Carr's first TD run put the Trojans ahead midway through the fourth, Western Michigan's Darius Phillips returned the ensuing kickoff 100 yards for a tying touchdown with 7:54 to play. USC then gained 79 yards on two big plays, with Deontay Burnett making a 42-yard catch before the speedy Jones' third TD run.
"Whoo, their running backs are special, you know what I mean?" Lester said. "We had to stop the run, and that was the frustrating part toward the end."
Western Michigan: The best season in school history just might get a worthy sequel. The Broncos had absolutely no problem hanging with the defending Rose Bowl champions, and could have won it with a few defensive stops in the second-half heat. The passing game has work to do, but Wassink is off to a promising start.
USC: While the offense finally came uncorked with a huge second half, the Trojans had difficulty stopping Western Michigan's impressive running game, which racked up 263 yards. With power-running Stanford headed to the Coliseum next weekend, USC's defense has plenty of work to do if it hopes to avoid getting flattened during Pac-12 play.
Wassink went 11 for 22, but made several big plays in his first career start as the replacement for Terrell, the Broncos' career passing leader. Wassink hadn't played a competitive game since his 2014 high school state final, but he caught the back end of a double pass and took it 27 yards in front of USC's stunned fans to take a lead shortly after halftime.
Jake Olson, the Trojans' blind long-snapper, made his USC debut when he delivered the snap for the final extra point. The remarkable moment was the culmination the remarkable dedication to football shown by Olson, who completely lost his sight eight years ago, but never gave up on his football dreams. "What a pressure player," Helton said. "Was that not a perfect snap?"
Western Michigan: The Broncos visit Michigan State.
USC: Stanford and its vaunted running game visit the Coliseum.
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