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SAN DIEGO -- The San Diego Chargers have regained their December swagger, thanks to Vincent Jackson's return and a smash-mouth defense.

Jackson caught a career-high three touchdown passes, Philip Rivers surpassed 4,000 yards passing for the third straight season and the Chargers beat Alex Smith and the San Francisco 49ers 34-7 on Thursday night to stay alive in the AFC West race.

Jackson reminded the Chargers just what they missed when he sat out 10 games during a nasty contract dispute.

"Since I've been here, it's like I had never left," said Jackson, who had his first three TD grabs of the season, of 58, 11 and 21 yards.

"He seems to be in midseason form," Rivers said. "I feel like he's been here for 15 weeks. That's a credit to the way he practices."

The Chargers (8-6) pulled within a half-game of the AFC West-leading Kansas City Chiefs (8-5), who lost 31-0 at San Diego on Sunday.

San Francisco was probably the toughest test left for the Chargers, who finish with games at Cincinnati (2-11) and Denver (3-10). If San Diego wins out and the Chiefs lose once, the Chargers will win their fifth straight division title.

The Chargers came within 4:26 of having consecutive shutouts for the first time in their 51-year history.

The 49ers (5-9) could wind up 7-9 and in a three-way tie and still win the NFC West, the NFL's weakest division.

Rivers and Jackson came out early in the fourth quarter and the Chargers leading 31-0.

Rivers was 19-of-25 for 273 yards, giving him 4,141 for the season. He tied Hall of Famer Dan Fouts' team record set from 1979-81. Jackson had five catches for 112 yards.

"He and Phil have such a good rapport," center Nick Hardwick said. "They both know what's going on, and they've studied for hours together. We were expecting him to come in and explode, and that's what he's done. He's a beast. He does things other players can't do, and he did it tonight."

Unhappy that the Chargers didn't give him a long-term deal, Jackson sat out the first seven games. He then missed three more games while serving a team-imposed suspension. The move cost him some $3 million in salary.

When he returned at Indianapolis on Nov. 28, he pulled a calf muscle two plays in and was done for the night and the next game.

On the fourth play from scrimmage, Rivers wound up and threw deep. The 6-foot-5 Jackson slowed down and reached out over 6-foot Nate Clements' head to make the catch at about the 15 before outracing the cornerback into the end zone.

Jackson exploited a mismatch against linebacker Takeo Spikes for an easy 11-yard catch just before halftime.

Jackson pulled in a 21-yarder early in the fourth quarter, getting the ball just past the pylon. The play was upheld after a review.

Mike Tolbert had a 1-yard TD run in the third quarter and Nate Kaeding kicked field goals of 25 and 39 yards.

Smith fell far short of having the happy homecoming he was hoping for. Coming off a promising return following a five-game absence, he was 19-of-29 for 165 yards with one interception and was sacked six times.

"We wanted it bad," linebacker Brandon Siler said of the shutout that just eluded the Bolts. "We were saying on the sideline, 'Don't give up anything cheap.' It hurts a little bit, but I think we already know we're a good defense. We proved that."

San Francisco's only score came on Brian Westbrook's 3-yard run with 4:26 left.

The 49ers watched as both a field goal and a touchdown came off the scoreboard in a span of four plays early in the second quarter.

Jeff Reed kicked a 38-yard field goal but San Diego's Antonio Garay was whistled for unnecessary roughness for trying to gain leverage, giving the 49ers first-and-goal at the 10. Smith scrambled and dived at the left pylon on third down and it was ruled a touchdown. The Chargers challenged and it was reversed, with Smith ruled down inches from the goal line. On fourth down at the 1, Siler threw Anthony Dixon for a 2-yard loss.

"I just read the play and got in there," Siler said. "I think it takes the energy and the momentum out of a team when you do something like that."

Said Smith: "It continued to get one-dimensional for us. When you play a defense of that caliber, they're the No. 1 defense for a reason. They played well."

Smith was playing against his hometown Chargers for the first time in the regular season.

Michael Crabtree had just three catches for 17 yards and Pro Bowl tight end Vernon Davis didn't have a catch until the waning minutes, finishing with one for 4 yards.

"This team has highs and lows, but if we are fortunate enough to go to the playoffs, I think we deserve to go," 49ers coach Mike Singletary said.

Game notes

The Chargers tied the team record for consecutive shutout quarters at seven. ... 49ers defensive tackle Justin Smith was ejected after making contact with umpire Garth DeFelice following a play. The lineman was in an argument with at least one Chargers player when he appeared to shove DeFelice, who was trying to keep him out of the scuffle.