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SAN DIEGO -- Matt Cassel didn't even see Eric Weddle, the San Diego Chargers' $40 million free safety.

That was the difference between the Kansas City Chiefs having a chance at a huge upset -- or at the very least, to get the game into overtime -- and a third straight loss.

Weddle intercepted Cassel on a screen pass at midfield with 55 seconds left, and the lethargic Chargers held on for a 20-17 victory over the winless Chiefs on Sunday.

"In the end, we made the play and they didn't," Weddle said. "It's huge. We definitely didn't want to lose this game."

Neither did the Chiefs, who were outscored a combined 89-10 in their first two games and were without stars Jamaal Charles, Eric Berry and Tony Moeaki, out with season-ending knee injuries.

"Those were the highs and lows of football," Cassel said. "One minute you feel good with a 20-yard gain close to field goal range and great position, and then on the next play the game's over."

Ryan Mathews scored twice, and the Chargers overcame two more interceptions by Philip Rivers to improve to 2-1 for just the second time in Norv Turner's five seasons as coach.

The Chiefs, who last year ended the Chargers' four-year run as AFC West champions, got the ball back at their 33 with 1:26 left after Rivers was stuffed on fourth-and-1 at the Chiefs 34. Out of timeouts, Cassel threw for 23 yards to Leonard Pope to get into Chargers territory. On the next play, Cassel, under pressure and backpedaling, threw the ball right to the blitzing Weddle, who signed a $40 million contract in the offseason.

Although he was blitzing, Weddle said he read that it was a screen play, with running back Dexter McCluster as the intended receiver, so he backed up.

"I knew something was up," Weddle said. "That's why I stopped. I knew the ball was coming my way. I read the play, read the quarterback and he threw it right there."

Said Cassel: "It was a screen pass. You try to keep your head downfield. When I swung back around I thought I could get it in there to Dexter. Obviously it's one I'd like to have back."

McCluster thought the Chiefs could make a big play on the screen.

"I thought he was blitzing, but at the last second he saw it and backed up, which led him to the interception," he said.

The Chiefs looked awful in the first half but the Chargers let them hang around.

Kansas City didn't get a first down until its opening drive of the second half, when Cassel threw a 4-yard TD pass to Dwayne Bowe to pull to 10-7.

The Chargers responded with an 80-yard drive capped by Mathews' run to the right side for a 10-point lead.

After the teams traded field goals, the Chiefs pulled to 20-17 when Cassel found Pope on a 1-yard scoring pass with 4:58 to play.

The Chiefs were out of timeouts, and all the Chargers had to do was run out the clock. They went for it on fourth-and-1 from the Kansas City 34, and Rivers was stopped to give the Chiefs a final chance.

Mathews ran 21 times for 98 yards. Rivers was 24 of 38 for 266, his lowest total of the season. Cassel was 17 of 24 for 176 yards, two touchdowns and the one INT.

Rivers has thrown two interceptions in each of the first three games. Kendrick Lewis picked off Rivers and returned it 50 yards. The Chiefs got 15 more yards for unsportsmanlike conduct after a referee ran into a Chargers player on the sideline who was too close to the field. The Chiefs got to the San Diego 11 before a holding penalty pushed them back, and Ryan Succop was wide right on a 38-yard field goal attempt.

Brandon Flowers had the other interception for Kansas City, along with a 43-yard return. He hurt his right knee on the play.

"Certainly I need to play better, and I'm going to work like crazy to do that," Rivers said. "But 2-1 is what's important."

Rivers also fumbled on San Diego's second drive, but center Nick Hardwick recovered. Two plays later, Mathews scored on a 2-yard run.

"We're not in sync in terms of playing the entire game with the rhythm that we'd like. That's going to come," Turner said.

Nick Novak kicked field goals of 35 and 41 yards for the Chargers. Succop kicked a 33-yarder for the Chiefs.

Game notes

The Chargers were without tight end Antonio Gates (foot), strong safety Bob Sanders (knee) and rookie defensive end Corey Liuget (ankle). ... Flowers said he hoped he could play next week against Minnesota. ... San Diego CB Quentin Jammer (hamstring), defensive linemen Jacques Cesaire (knee) and Antonio Garay (head) were hurt in the fourth quarter.