The Golden Eagles (5-6, 3-4 Conference USA) won their third consecutive game and ended East Carolina's three-game winning streak. Southern Miss, which lost five straight games earlier this season, needs a win over Southern Methodist in its final regular season game on Nov. 29 to become bowl eligible.
The Pirates (6-4, 4-2) also failed to clinch at least a share of the Conference USA East title and their first trip to the league title game.
Damion Fletcher, Southern Miss' all-time leading rusher, ran for 121 yards on 23 carries and one touchdown in his first game after missing two games with a hamstring injury.
Davis hit Brown one play after Justin Wilson picked off a pass deep in Golden Eagles territory. The scoring play gave Southern Miss a 21-3 lead with 11:37 to play.
Southern Miss took a 7-3 lead into halftime on Davis' 20-yard touchdown pass to Leroy Banks with 4:35 left in the second quarter.
East Carolina took a 3-0 lead early in the quarter on Ben Hartman's 32-yard field goal. Hartman also missed a pair of field goals in the first half.
Davis was 18 of 30 for 239 yards and two scores. Brown had eight catches for 124 yards and needs just three more receptions to tie the school's single season record of 66.
Wilson picked off another pass late in the game to end any hopes of a comeback. East Carolina's Patrick Pickney had thrown just three interceptions in the first nine games.
South Carolina football players will wear stickers on their helmets this season to honor the nine people who died in a shooting at Emanuel AME Church in Charleston this past June.
Washington has found its starting quarterback, but coach Chris Petersen said the Huskies will keep that information under wraps until Friday's season opener at No. 23 Boise State.
Joey Counts scored on a 1-yard run on fourth-and-goal with 2 seconds left to give Montana a 38-35 victory over four-time defending FCS champion North Dakota State on Saturday.
Transfer Vernon Adams will be the starting quarterback when Oregon begins its season against Eastern Washington on Sept. 5.
Tim Beckman is threatening legal action after Illinois fired him as football coach Friday amid allegations of influencing medical decisions and pressuring players to play hurt.
LSU offensive coordinator Cam Cameron revealed in a post-practice news conference that he has been treated for prostate cancer but plans to coach this season.