Lambo's kick got tipped at the line of scrimmage and still cleared the crossbar. The former soccer player ran the other way and slid on both knees near midfield before getting mobbed by teammates.
It gave Jacksonville its first three-game winning streak since 2013.
The game ended up in overtime after a wild and wacky final two minutes of regulation that included a fumble, two interceptions, a taunting penalty and a costly flag for roughing the passer. At times, it looked as if neither team wanted to win.
After all the chaos, Lambo drilled a 34-yard field goal to send it to the extra period.
After Jacksonville punted, A.J. Bouye intercepted a pass from Philip Rivers on third down and returned it to the 2-yard line. But a taunting call on cornerback Aaron Colvin pushed the Jaguars (6-3) back 15 yards. Lambo hit the winner a few plays later.
Colvin's penalty was just the last in a crazy series of poor decisions for both teams. Jaguars receiver Marqise Lee was called for taunting in regulation, and Chargers defensive end Joey Bosa was flagged for unnecessary roughness that set up the game-tying kick in regulation.
On top of those, Chargers rookie Austin Ekeler fumbled while trying to run out the clock with a three-point lead, and Blake Bortles threw two interceptions while trying to rally the Jaguars in the final two minutes.
Bortles completed 28 of 51 passes for 273 yards, with a touchdown and the two picks. Leonard Fournette ran for 33 yards on 17 carries and failed to score for the first time in his rookie season.
Rivers threw for 235 yards and two scores, both to Ekeler, but his interception proved to be the most costly of all the late-game mistakes.
The Chargers (3-6) lost for the first time in seven games in the series.
The Jaguars scored on a fake punt and on a drive that included 11 consecutive passes from Bortles.
Corey Grant took a direct snap on a fourth-and-7 play, juked one defender, made another miss and then zigzagged his way for a 56-yard touchdown in the first quarter. It was the second straight week Jacksonville got a huge play from special teams. Jaydon Mickens returned a punt 63 yards for a touchdown in a victory against Cincinnati last week.
With the NFL's top running game stalled, the Jags turned to Bortles. He threw a perfect pass to Marqise Lee for a 6-yard score in the third and then found his top receiver for a 2-point conversation that tied the game at 14.
After the two interceptions late, Bortles directed the game-tying drive at the end of regulation.
Jaguars receiver Allen Hurns was carried to the locker room with a right leg injury late in regulation. ... Jaguars special teams ace Arrelious Benn injured his right knee in the first half and was later ruled out. ... Jaguars lost long-snapper Matt Overton (right shoulder) in the fourth quarter. ... Both teams played without their starting right tackle. Los Angeles' Joe Barksdale (foot) and Jacksonville's Jermey Parnell (knee) missed the game after being listed as questionable Friday.
Former Jaguars head coach and current Chargers defensive coordinator Gus Bradley returned to Jacksonville 11 months after being fired. Bradley, who went 14-48 in three-plus seasons in Jacksonville, avoided most pre-game contact with former players and assistants. A few Jaguars coaches tracked down Bradley on the opposite side of the field, but it was clear Bradley wanted to save any reunions for after the game.
Chargers: Host Buffalo next Sunday, the first of three home games in four weeks.
Jaguars: Play at winless Cleveland next Sunday, the first of two straight on the road.
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