San Diego, who snuck into the playoffs on the final day of the regular NFL season, took advantage of three second-half turnovers from Andy Dalton to upset Cincinnati 27-10 on Sunday.
And in the National Conference wildcard game, the San Francisco 49ers used a 33-yard field goal as time ran out to edge the Green Bay Packers 23-20.
Chargers quarterback Philip Rivers played mistake-free ball in his team's surprising wild card round victory, which allows San Diego to advance to the next round where they will face the top-seeded Broncos in Denver.
"It was an outstanding team effort," said first-year Chargers head coach Mike McCoy.
"We knew it was going to be a slugfest from the first snap all the way through the game."
Rivers threw for a modest 128 yards but connected with Ladarius Green for the go-ahead touchdown in the third quarter that began a run of 20 unanswered points for the Chargers.
The loss was the first at home all season for the Bengals, whose post-season misery continues. Cincinnati has not won a playoff contest since 1991.
Dalton's game took a turn for the worse when it started snowing at Paul Brown Stadium on Sunday. The Bengals quarterback threw two interceptions and lost a fumble.
"It's disappointing. All the good stuff we did this year, to come out and not win this game, it hurts," said Dalton, who has lost all three of his post-season starts.
"We didn't do enough to win."
The Chargers had everything go their way in week 17, as the Bengals beat the Baltimore Ravens, the New York Jets beat the Miami Dolphins and they upended the Kansas City Chiefs in overtime to claim the AFC's final wildcard spot.
The Chargers struggled on offence in the second quarter on Sunday, failing to even gain a first down.
But San Diego took a 14-10 lead with 6:46 remaining in the third by using a combination of passes and runs during a 10-play, 80-yard drive.
Green caught a four-yard pass from Rivers in the corner of the end zone and the Chargers settled for a pair field goals following two Dalton turnovers to extend the lead.
Ronnie Brown help seal the victory with a late 58-yard touchdown run for the Chargers.
San Francisco kicker Phil Dawson booted a 33-yard field goal as time expired to lift the 49ers to a win over the host Packers in frigid winter conditions at Lambeau Field.
It marked the second consecutive season the 49ers eliminated the Packers in playoffs.
Green Bay kicker Mason Crosby drilled a game-tying 24-yard field goal with just over five minutes to play.
The 49ers advance to play Carolina in the divisional round next Sunday.
"It is win or go home so everyone is going to leave it on the line," said San Francisco linebacker NaVorro Bowman.
