The Broncos (4-1) won their fourth straight by intercepting Golden Eagles quarterback Ricky Lloyd twice and recovering three of four fumbles by Southern Miss, which is 0-5 for the first time since 1976.
The 5-1 edge in turnovers came one week after coach Chris Peterson's team used three New Mexico fumbles to survive a 32-29 scare.
"I don't know how we keep getting turnovers," Peterson said. "But it sure makes things different for us. I'm not sure why we're getting them -- whether we're just in the right place at the right time or what -- but as long as they are coming like they did today, we're going to be in every game and we have a chance to win most of them."
The first interception came on Lloyd's fifth attempt of the game and set up Southwick's 11-yard scoring pass to Matt Miller that put the Broncos on top 7-0. Linebacker Tyler Gray returned his first-career interception 34 yards to the Golden Eagle 11-yard line, and Southwick and Miller connected on the ensuing play.
The lead swelled to 24-0 at the half when another Southern Miss turnover set up Southwick's second touchdown, a 33-yard strike to Chris Potter with 6 seconds left in the second quarter. That proved to be an insurmountable deficit for the Golden Eagles, who came into Saturday ranked 119th in the country in total offense.
"That was nice to get that score there," Southwick said. "We got the ball back after another turnover, and we're thinking, 'Let's just get into field goal range.' Luckily, (Potter) was able to get free and get some separation. I didn't think he had moves like that."
Southern Miss' two touchdown drives came on consecutive possessions in the third and fourth quarters after Anthony Alford replaced Lloyd at quarterback, but the Broncos answered both touchdowns with scores of their own.
Southwick connected with Kirby Moore for 27 yards and his third touchdown pass to make it 37-7, and Michael Frisina added his second field goal of the afternoon from 31 yards out with less than three minutes left to close out the game.
Southwick finished 17-of-26 passing for 201 yards with an interception.
D.J. Harper led the Broncos in rushing with 14 carries for 51 yards, including touchdown runs of 11 and 19 yards.
South Carolina coach Steve Spurrier told his players and coaches Monday night that he is retiring immediately, sources told ESPN.com.
Steve Sarkisian has been plagued of late by apparent substance-related circumstances, including arriving to team facilities appearing intoxicated Sunday, according to sources.
Florida Gators quarterback Will Grier has been suspended for the year after testing positive for a performance-enhancing substance found in a supplement, coach Jim McElwain announced Monday.
Former USC coach Pete Carroll said Monday that he's saddened by Steve Sarkisian's situation and he has reached out to his former assistant.
Ole Miss offensive tackle Laremy Tunsil will be eligible to return to action for the Rebels following Saturday's game against Memphis, sources told ESPN.com on Monday.
After a decades-long ban, Nevada Gaming Control granted approval for the state's regulated sportsbooks to offer wagering on the Heisman Trophy, with LSU's Leonard Fournette the early favorite.