Asked if he'd ever been a part of such a big comeback, Carter replied: "Only in Pop Warner football."
It took a quarterback of Manning's caliber to pull this one out.
"It sure was special considering what was on the line," said Manning, a Super Bowl winner and four-time NFL MVP who's in his first season with the Broncos.
Manning was 13 of 14 for 167 yards in the second half for the Broncos (3-3) who tied the Chargers (3-3) atop the AFC West.
It tied for the fourth-biggest regular-season comeback in NFL history.
Manning had been 1-5 in his last six games against San Diego, all with Indianapolis.
Rivers was intercepted four times three in the fourth quarter and lost two fumbles. The four pickoffs and six turnovers were both career highs.
A week earlier, the Chargers blew a 10-point lead in the third quarter in a 31-24 loss at New Orleans.
"When you lose it's rough, especially in a game where you had a big lead and so much at stake," Rivers said.
"It's bad," San Diego linebacker Takeo Spikes said. "Every adjective you can come up with as far as disappointment, it covers it."
The Broncos seemed finished after an awful first half in which Manning served up an 80-yard interception return for a touchdown by Quentin Jammer and two special teams fumbles led to 10 points for the Chargers.
"I thought we had a good plan. It was so disappointing to have these special team mistakes," Manning said.
Manning began the comeback when he hit Demaryius Thomas on a 29-yard touchdown pass on the opening drive of the second half.
On the ensuing San Diego possession, Elvis Dumervil stripped the ball from Rivers and Carter ran 65 yards for a touchdown, holding up the ball in celebration as he approached the end zone.
Denver then sacked Rivers to force a punt and Manning capped the next drive with a 7-yard touchdown pass to Eric Decker to pull to 24-21.
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.
That score was set up by Carter's interception.
Harris sealed the victory with a 46-yard interception return for a touchdown with 2:05 left. It was his second pick of the game.
"This was as good a second half of football as I've been involved in," Broncos coach John Fox said.
As for Manning, "He's real high on my list," the coach said. "He performed very well and has performed well in the last four games. He's going to keep getting better and better."
Manning finished 24 of 30 for 309 yards with one interception.
"Regular-season game, I think this is the best," said Stokley, who was a teammate of Manning's with the Colts. "The second half was unbelievable. We needed to win big-time and to perform like he did, it was awesome."
Fox said there "were no mystery words of wisdom at halftime. "Given how poorly we played in the first half, we just said we could play better in the second half and we broke out of it."
"We came out in the second half, everybody was accountable and professional," he said. "We had 30 minutes and I thought it was important to get off to a good start with that first drive. Hitting DT for the touchdown really set the tempo for the second half."
Both teams head into their bye week.
"We feel fortunate to be tied for first place in our division at 3-3," Manning said. "It's going to be a competitive division down the stretch. There are some things we can improve on and we'll use the bye week to do that."
Jammer intercepted Manning and returned it 80 yards for his first career touchdown, and Antonio Gates caught his second TD pass of the game in the second quarter, extending the Chargers' lead to 24-0.
Before Jammer's TD, the Broncos appeared on their way to their first score of the game with Manning's 55-yard pass to a wide-open Decker. But Decker tripped himself at the Chargers' 40, got up and was tackled at the 30-yard line.
Manning clapped both hands to his helmet in disbelief, one of several times the star quarterback expressed frustration.
"A piece of grass made a nice tackle," Manning joked. "Those kind of plays happen. You do kind of wonder, is this not meant to happen? Obviously Decker was sick about it.
"It's about playing 60 minutes. There's no quit in this team," Manning said.
Three plays later, Manning threw a pass straight to Jammer. Manning made a weak effort at a tackle as Jammer went speeding by.
Rivers was 25 of 41 for 242 yards.
"Right now we're not able to put together a complete game," San Diego coach Norv Turner said. Game notes
The Chargers' 24-0 halftime lead was their largest since taking a 28-0 halftime lead against the St. Louis Cardinals on Sept. 20, 1987. The Bolts held on to win that game, 28-24.
Gates had TD catches of 15 and 11 yards and Nick Novak kicked a 32-yard field goal for San Diego in the first half.
Decker had six catches for 98 yards, while Gates had six catches for 81 yards.