Rivers' harried heave from the 25-yard line was swatted down in the end zone by Brent Grimes, and the Miami Dolphins beat mistake-prone San Diego 20-16 Sunday.
The Chargers (4-6) dropped their third game in a row to further hurt their chances of an AFC wild-card berth. They've lost three games by four points or less, and another game in overtime.
"We made too many mistakes from start to finish," coach Mike McCoy said. "We hurt ourselves way too much."
Rivers threw for 298 yards and Ryan Mathews ran for 127, including a career-best, 51-yard dash to set up a field goal. But the Chargers had 10 penalties for 76 yards, including two infractions that cost them 11 points in the first half.
"Ten penalties, that's a lot," Rivers said. "We're not playing well enough to overcome those things."
They nearly did. Trailing by four points, the Chargers started from their own 17 with 1:54 left and drove to the Miami 25. On the final play, Rivers lofted a pass toward Vincent Brown in the end zone, but the 5-foot-10 Grimes leaped to slap the ball away.
Earlier threats ended at the Miami 5, 11 and 32.
"We didn't capitalize on our opportunities," Rivers said. "When we had a chance to score in the red zone, we didn't."
Miami's Ryan Tannehill threw for 268 yards, including a 39-yard score to Charles Clay, who broke two tackles on the play. Miami managed 104 yards rushing behind a makeshift line.
The Dolphins' victory came amid a harassment scandal that raised questions regarding the team's locker room culture. An NFL special investigator will question players this week about the relationship between offensive tackle Jonathan Martin and guard Richie Incognito.
"There's a lot going on, but we're not focused on that," Tannehill said. "We're focused on football."
The Dolphins (5-5) won for only the second time in the past seven games. They're still in contention for an AFC wild-card berth, despite a dreadful defeat last Monday at Tampa Bay and the distractions of the harassment case.
"We're fighting through this," tackle Tyson Clabo said. "Someone's got to get that last wild-card spot. Why not us?"
Miami played at home for the first time since the scandal broke. The stands were less than two-thirds full, and an airplane banner reflected the mood by calling for the firing of general manager Jeff Ireland, who has long been in disfavor with fans.
Because center Mike Pouncey missed the game with an illness, the Dolphins had three backups starting on the offensive line. Martin missed his third consecutive game while undergoing treatment for emotional issues, and the suspended Incognito sat out his second game.
Working behind the patchwork line, Tannehill was sacked four times, increasing NFL-high season total to 41. But Miami averaged 5.5 yards per rush to limit the Chargers' time of possession.
Penalties repeatedly hurt the Chargers. Corey Liuget was flagged for roughing the passer to negate a teammate's fumble recovery at the San Diego 1, and two plays later the Dolphins scored a touchdown for a 10-7 lead.
Liuget said he didn't see Tannehill get rid of the ball.
"It was a costly penalty for us," Liuget said. "I wish I could get that one back. It's not a great feeling at all."
A scrambling Rivers hit Antonio Gates for a 5-yard touchdown with a minute left in the first half, but the quarterback was flagged for throwing past the line of scrimmage, and the Chargers settled for a field goal that made it 10-all at halftime.
A drive in the second half stalled after receiver Keenan Allen was flagged 15 yards for taunting, and the Chargers defense was penalized four times for offsides.
San Diego's Derek Cox dropped a potential pick-six in the first quarter, and on the next play Johnny Patrick intercepted Tannehill at midfield. The Chargers scored four plays later for a 7-3 lead.
Clay put Miami ahead to stay in the third quarter when he caught a short pass and ran over defenders Marcus Gilchrist and Donald Butler en route to the end zone, making it 17-10.
Safety Eric Weddle later shook his head recalling the touchdown.
"Seven missed tackles," he said, exaggerating slightly.
Notes: Chargers CB Johnny Patrick missed the second half with a head injury. ... Dolphins CB Dimitri Patterson left the game in the first half when he aggravated the groin injury that has bothered him for much of the season. ... The Chargers have lost seven in a row in Miami since their memorable 41-38 overtime playoff victory in January 1982.