Trailing 10-7 at the half, the Chargers made Bengals quarterback Andy Dalton pay dearly for his miscues, two interceptions and a fumble, to hand Cincinnati their first home loss this season.
"We asked a lot of our defense today, they came up with three big turnovers, we needed to convert those into touchdowns and we didn't but we did enough," said Chargers quarterback Philip Rivers. "We didn't turn it over and that is key, it always is in playoff games and then the weather got bad.
"When you have a lead and the weather turns, it's in your favor."
For the AFC North champion Bengals it was another shocking end to a promising season as their run without a playoff win extended to a painful 23 years.
Four times in the last five seasons Cincinnati has appeared in a wild-card contest and fallen flat, losing twice to the Houston Texans (2012, 2011), the New York Jets (2009) and San Diego.
"Obviously the biggest difference was turnovers," offered a dejected Bengals head coach Marvin Lewis, who is winless in five trips to the playoffs since taking over as head coach in 2003. "It's tough. It's a tough day.
"It's disappointing, as hard as we've worked and played, to have a football game where we had opportunities and we let it go.
"When you turn the ball over like we did today, that keeps you from scoring."
San Diego outscored Cincinnati 20-0 in the second half but it was far from a dominating display by the Chargers offense as Dalton passed for 334 yards, nearly three times as many as Rivers, who had a modest outing completing 12-of-16 passes for 128 yards and one touchdown.
But Rivers was mistake free while Dalton and the Bengals committed a total of four turnovers.
It was the fifth straight win for the Chargers who will carry building momentum into Denver next Sunday to take on Peyton Manning and the top-seeded Broncos.
"We talked all week about this being the fifth round, so the sixth round will be next Sunday in Denver. We've been in that (must win) mode for five weeks now. We know what's in front of us, Denver is an awesome team," said Rivers. "We were able to win there a few weeks ago, so we'll be confident but it is going to be a tough task."
The Chargers were first onto the scoreboard, Rivers engineering a time-consuming 86-yard drive that chomped up nearly half the opening quarter and was capped off by the diminutive Danny Woodhead darting over from the five.
Cincinnati answered back with a time-crunching drive of their own in the second, Dalton marching his team 60 yards before tossing his first career post-season touchdown pass to Jermaine Gresham.
The Bengals had opportunities to pull away later in the quarter when they fumbled inside the San Diego five but still took a 10-7 lead into the intermission on Mike Nugent's 46-yard field goal on the final play of the half.
Rivers, who attempted only six passes in a conservative first half, opened things up in the third quarter, completing six-of-six passes including a four-yard strike to Ladarius Green, to jump in front 14-10.
A pair of Dalton miscues, a fumble and an interception, deep in Bengals territory allowed the Chargers to add to their lead going up 20-10 on two short Nick Novak field goals.
With the Bengals on the march in the fourth quarter, Dalton was again intercepted, snuffing out yet another scoring chance.
Ronnie Brown then put the game out of reach with a 58-yard touchdown romp to end a wet and miserable day at dreary Paul Brown Stadium.
'We knew it was going to be a slugfest," said Chargers coach Mike McCoy. "The defense played lights out in second half, really the whole game.
"They did a great job, create turnovers, the fourth down stops, a number of big plays from a lot of different players.
"We're going to take it one week at a time and just keep going."