USC’s surprising depth has been a key to its even more surprising 15-1 start

USC was lagging midway through the first half against Stanford on Thursday when it received a kick from a full-court press and an unlikely source.

Jonah Mathews, USC’s freshman guard, swarmed Stanford’s guard, intercepted a lazy pass, and converted it for a layup. On the very next possession, Mathews baited a different player into a false sense of security, then darted to snatch another pass away and set up another score.

USC surged, then sunk back into disinterest. Shortly before halftime, USC’s lead was only one point when Mathews camped out in the corner, caught a pass and sunk a momentum-shifting three-pointer.

No. 25 USC, which will play California on Sunday, has stunned even itself with a 15-1 (2-1 Pac-12) start. With forward Bennie Boatwright injured, the fast start has required major growth from its big three starters: Jordan McLaughlin, Elijah Stewart and Chimezie Metu. But USC also owes several of its wins to an unlikely area of strength: the bench.

“When you have a key player out for this long, everyone gets their chance,” Coach Andy Enfield said. “We have to mix and match.”

USC’s departures in the off-season — two to the NBA, four to transfers — didn’t gut the starting lineup but appeared to leave USC’s depth devastated. That has not been the case. USC has averaged 20 points per game off the bench, four more points than its opponents.

Mathews has averaged 7.4 points. Freshman De’Anthony Melton, who has often come off the bench, has averaged 10.1 points, 5.4 rebounds and three assists.

Their impact has been felt most acutely on defense. Enfield called Melton the team’s best all-around defender. Mathews, he said, was the best on-ball defender. Charles Buggs, a graduate transfer forward, said he views his role as mostly defensive.

“I first came here, my main thing was not defense,” Mathews said. “It was scoring the basketball.”

But he said he soon realized “defense is the key to playing time.”

Boatwright’s injury often obliged USC to use a four-guard lineup, which has caused trouble in halfcourt defense. But it has been lethal in a press, like the one USC used against Stanford, when it can use its guards’ speed and length.

Sunday’s game will require their defensive skills. California (10-5, 1-2) has given up 61.7 points per game this season, second-fewest in the Pac-12. With points at a premium, USC cannot allow the Bears to score in bunches.

The depth also affords Enfield some flexibility to match up against an opponent. He has shuffled the starting lineup recently, shifting between big and small rotations. Initially, Nick Rakocevic, another freshman, started in Boatwright’s position. His limited production, and USC’s pattern of slow starts, led Enfield to replace him with Melton. Against Stanford, Rakocevic was back in, replacing guard Shaqquan Aaron, who became another effective bench player, with 9.7 points and 3.6 rebounds per game.

“Our team’s really deep, so you just go out there and play hard for as long as you’re out there, and if you need a sub you tell Coach,” Metu said. “You have confidence that the next guy he puts in is going to produce.”

NEXT UP

USC VS. STANFORD

When: 7 p.m., Sunday

Where: Galen Center.

On the air: TV: ESPNU. Radio: 690.

Update: USC has lacked an identity without forward Bennie Boatwright but has scrapped to wins in a variety of ways this season. Recently, it has been with defense: Its three Pac-12 games have been among its four worst scoring nights this season, but it has started 2-1.

The Bears prefer to win with defense too. California has given up 70 points or more just twice this season, against San Diego State and UCLA, which defeated the Bears, 81-71, on Thursday.

Offense has been more of an issue. California ranks 10th in the Pac-12 in scoring offense, at 70.9 points per game. Forward Ivan Rabb leads the team with 15.3 points per game and guard Charlie Moore contributes 15.1.

zach.helfand@latimes.com

Follow Zach Helfand on Twitter @zhelfand