They had trailed Kansas City the whole game, but with the ball at the Chiefs 15-yard line and Nick Novak's right leg warmed up, they were poised to escape with a win on the road.
Then everything went wrong.
The ball squirted loose before it ever got in Rivers' hands, and a scrum quickly ensued. By the time all the bodies were dragged off the pile, Chiefs linebacker Andy Studebaker was running toward the sideline, joyfully holding the ball over his head.
The game headed for overtime, and Ryan Succop eventually knocked through a 30-yard field goal to give Kansas City a dramatic 23-20 victory Monday night.
"It looked to me like Philip got a little anxious and came out early," Chargers coach Norv Turner said gloomily. "That's a very unusual way to not win a game."
Kansas City (4-3) became the first team in NFL history to lose its first three games and share at least part of a division lead after four more. The Chiefs are also the first team since the Pittsburgh Steelers in 2000 to win four straight games after losing their first three.
Rivers could have prevented all of it from happening.
"I haven't had one in years," he said of the fumbled snap. "It's unfortunate. I dropped it. This one is rough. You blow it on a play that never should have happened."
Kansas City had its own chance to win in regulation, but Matt Cassel overthrew his wide receiver in Chargers territory and Eric Weddle's second interception sent the game to overtime.
San Diego won the toss but failed to pick up a first down, and Cassel calmly led Kansas City down field. Succop's field goal with 5:16 remaining gave the Chiefs their fourth straight win and moved them into a tie with San Diego (4-3) and the idle Oakland Raiders (4-3) in the division.
"We were saying, 'Don't quit,'" Studebaker said. "You never quit, even if it looks ugly. If you quit every time something looks ugly, you miss an opportunity to do something special."
Boy, was this one ever ugly.
Rivers wound up throwing for 369 yards, but he also had two interceptions and one big fumble.
The teams combined for eight turnovers, matching the most in an NFL game this season. The Chargers were called for 12 penalties worth 105 yards in a gruesome game on Halloween night.
One that looked pretty in the end to Kansas City.
Meanwhile, things are unraveling for the Chargers, who won four of their first five games.
They were leading the New York Jets 21-10 at halftime last week before Rivers, who has struggled mightily this season, tossed two fourth-quarter interceptions. The three-time Pro Bowl quarterback watched as the Jets scored the final 17 points to steal the win.
Now comes a disaster in Kansas City.
"It was a critical situation and it cost us," center Nick Hardwick said of the fumbled snap. "It's been six years and we haven't had one on the ground. We can't have that."
The Chiefs had things going their direction early, getting a 36-yard field goal from Succop in the first quarter and then capitalizing on Rivers' second interception in the first few minutes.
With the ball at the Chargers 39, Cassel dropped back to pass and saw Jonathan Baldwin streaking for the end zone. The wide receiver out-jumped fellow rookie Marcus Gilchrist for his first career touchdown catch, giving the Chiefs a 10-0 lead.
Novak kicked a field goal midway through the second quarter, but he missed another late in the quarter, and Succop hit one with just a few ticks on the clock for a 13-3 halftime lead.
The Chargers defense kept them in the game in the third quarter, holding the Chiefs to two three-and-outs and picking off Cassel. Kansas City only managed 44 yards of offense in the second and third quarters combined.
Novak kicked three field goals in the third quarter, drawing the Chargers within 13-12, but their inability to get into the end zone cost them dearly.
Kansas City finally got its offense in gear, marching 74 yards in 10 plays early in the fourth quarter. Jackie Battle finished off the drive by leaping over the scrum from a yard out, giving the Chiefs a 20-12 lead with 12:01 left.
It sure didn't last long.
Rivers completed four straight passes covering 74 yards — one for 27 to Vincent Jackson on third-and-13 — before Curtis Brinkley leaped in from 2 yards out for the Chargers' first touchdown.
Going for the 2-point conversion and the tie, Rivers floated a pass to Brinkley in the flat and he was thrown back by cornerback Brandon Carr. The officials ruled that Brinkley nudged the ball over the goal line, though, and the decision was upheld by video review.
It was the fourth replay call that went against the Chiefs.
Rivers' butterfingers made that a moot point.
"It was a great victory for us. What an unbelievable environment," Cassel said. "With the turnover late in the game, we had another opportunity, and we took advantage of it in overtime."
Notes: The Chargers signed LB Bront Bird from the practice squad and released WR Bryan Walters before the game. ... Chiefs S Jon McGraw left with a shoulder injury. ... San Diego CB Quentin Jammer left the game in the second half with cramps and RB Ryan Mathews left with a groin injury.