The 24-point rally tied for the fourth largest comeback in NFL history.
Manning was 13 of 14 for 167 yards in the second half for the Broncos (3-3) who tied the Chargers atop the AFC West.
Rivers was intercepted four times – three in the fourth quarter – and lost two fumbles.
Manning’s 21-yard touchdown pass to Brandon Stokley gave Denver its first lead of the game, 28-24 with 9:03 left. Stokley outleaped defensive back Marcus Gilchrist to catch the ball, and then got both feet down before tumbling out of the end zone.
Manning also had second-half touchdown passes to former Georgia Tech star Demaryius Thomas and Eric Decker, who led the Broncos with six catches for 98 yards.
Harris sealed the victory with a 46-yard interception return for a touchdown with 2:05 left. It was his second pick of the night.
Manning finished 24 of 30 for 309 yards with one interception.
Rivers was 25 of 41 for 242 yards and two touchdowns for the Chargers, who dropped to 3-3.