Rivers tried to guide San Diego back for a go-ahead touchdown, but he threw an interception to Denver’s Chris Harris and the Broncos’ defender raced 46 yards for a final touchdown with 2:05 remaining.
The Broncos have outscored all foes combined in the fourth quarter by 79-6 this season.
“We know we have to buckle down and make plays,” Decker said.
San Diego’s Quentin Jammer intercepted a Manning pass and returned 80 yards for a touchdown to give the Chargers a 17-0 lead in the second quarter. It was the first pickoff surrendered by Manning in more than 16 quarters of play.
Two other Denver turnovers set up first-quarter San Diego points, Nick Novak’s 32-yard field goal and a 15-yard touchdown pass from Rivers to Gates.