Rytan Kartje (LA Times)  —  His pass had just been picked off, a most unfortunate turn at a most unfortunate time for USC, when Jayden Maiava took off sprinting toward the pylon.

The past month to that point hadn’t been one to remember for the Trojans quarterback. The week before, at Nebraska, Maiava completed just nine passes. Two weeks before that, he struggled through a rain-soaked loss in South Bend. This interception was his sixth in five weeks — and a pass he surely preferred to have back.

But as Northwestern’s Najee Story rumbled toward that same pylon with ball in hand, USC’s quarterback closed in, lowered his shoulder and catapulted his entire body toward the 288-pound defensive tackle. On a Friday night filled with strange twists for the Trojans, who walked away with an 38-17 win over Northwestern, none was more consequential than that moment, as Maiava’s hit jostled the ball loose and it bounced in the end zone and out of bounds.

“Shoot,” Maiava said, “I just thought I’d go out there and sacrifice my body for my brothers.”

In this case, his sacrifice made all the difference. The fumble gave USC possession — and turned the tide in a game that the Trojans absolutely couldn’t afford to give away as they hang on to slim hopes of making the College Football Playoff.

It barely seemed to matter that Friday’s game-breaking moment began with a bad mistake from Maiava. Teammates were too in awe of their quarterback to remember that part.

“Just shows you what type of player he is,” USC wideout Makai Lemon said.

“He does everything,” added running back King Miller. “He’s Superman, you know?”

But it was USC’s defense that played hero from then on. A unit that seemed not long ago like a glaring problem for USC held Northwestern to just three points in the second half, the second time in two games the group allowed just a field goal after halftime.

“We just kind of got settled in,” safety Bishop Fitzgerald said. “We started stopping the run. We won early downs. So we got them off schedule.”

The schedule was its own issue coming in, after a shorter-than-usual turnaround from the Nebraska trip. But after halftime, none of the concerns that followed USC into Friday night would look as pressing by Saturday morning. Northwestern, after gashing the Trojans early on the ground, managed just 103 total yards in the second half.

Maiava also was much sharper as a passer. Aside from his second-quarter interception, Maiava completed 24 of his 33 passes for 299 yards and two touchdowns. More than half of that output came from Lemon, who bounced back from his worst week of the season to reel in 11 catches and a career-high 161 receiving yards. Fellow wideout Ja’Kobi Lane was nearly just as good with seven catches for 74 yards, including an acrobatic, one-handed score.

Once again, the Trojans’ offense benefited from a big performance from Miller, the walk-on-turned-starter who continues to thrive since taking over USC’s backfield. It was Miller who would make Northwestern pay after losing that fumble in the end zone in what amounted to a 14-point, second-quarter swing.

USC RB  King Miller skirts by NW defenders in the second half Friday at the Coliseum. (Eric Thayer / LAT)

On the very next play, Miller burst through a hole in Northwestern’s defense and sprinted 55 yards. Two plays later, he punched in a touchdown to give USC a 21-14 lead. It was the last points the Trojans would need to secure their fifth Big Ten victory of the season.

USC tried to set the tone right away with a 16-play opening drive. Maiava had nine completions on the first possession alone, capped by a touchdown to Lemon (6).

But after matching that with its own long touchdown drive, Northwestern immediately stopped USC for what appeared to be a three and out. The Trojans sent out the punt team.

Only after the fact would anyone notice that the player wearing the usual No. 80 worn by USC punter Sam Johnson was in this case backup quarterback Sam Huard, whose number had officially been changed from No. 7 weeks earlier, in anticipation of this particular call.

“We’ve got some creative guys on staff,” USC coach Lincoln Riley said.

The diabolical call paid off. Huard completed the fake punt pass for a first down. Five plays later, Maiava took off toward the end zone and punched it in for his team-leading sixth rushing score of the season.

Northwestern matched that effort, too, marching down the field behind running back Caleb Komolafe, who had 117 all-purpose yards in the first half alone. He finished with 158.

USC’s defense didn’t get its first stop until the final five minutes of the first half. But on the ensuing drive, Northwestern very nearly flipped the game on its head, as Maiava threw that pick in the middle of the field.