Updated

Derrick Johnson is ready to credit this rain-soaked September victory to those brutally hot two-a-days in August.

"We're a physical team throughout training camp and it paid off tonight," said Kansas City's veteran linebacker.

While Jamaal Charles and Dexter McCluster were grabbing the headlines with long touchdown plays for the Chiefs, Johnson was compiling a team-high 12 tackles in Monday night's 21-14 victory over San Diego.

Johnson's jolting hit on Chargers rookie Ryan Mathews caused a fumble which led directly to one of Kansas City's two offensive touchdowns of the game.

Not bad for someone who struggled all last year to regain his starting job.

"That's what I'm trying to prove. Every game, I'm trying to play with a chip on my shoulder," he said. "That's not a negative chip. That's a chip that keeps me on my toes at all times."

The Chargers, four-time defending AFC West champions, appeared ready to move in for a tie after Philip Rivers drove San Diego to a first-and-goal from the 4 with a little over 1 minute left.

On the final series, Rivers' first pass was incomplete, then Darren Sproles lost 2 yards on a stalled run. Another pass from Rivers sailed high. Then, with 39 seconds left, Rivers missed on fourth down, clinching the Chiefs' first Monday night victory in a decade.

On that final game-saving defensive play, Glenn Dorsey said the plan was to make Rivers throw from a spot he prefers to avoid.

"We wanted to get a push in the middle to force him to make a sporadic throw outside the pocket where he is not comfortable," said the Chiefs defensive end. "He did that. He started moving around and he wasn't able to set his feet. That's the biggest thing, trying to get pressure on him and holding up like we had been doing all night long."

San Diego's winning streak against the Chiefs ended at five games.

"They made some big plays in all three phases," Chargers coach Norv Turner said. "They handled the environment in terms of the weather conditions. I thought they did a good job in handling that, particularly in the second quarter.

"The disappointment for me comes obviously from our (kick) coverage teams. We think that should be a strength for us and something we work hard at."

Jamaal Charles had a 56-yard touchdown run after Rivers' 3-yard TD pass to Antonio Gates put the Chargers on the board first. Then, rookie Dexter McCluster, a training camp sensation with quickness and flair, broke a team-record by one yard with a 94-yard punt return for a 21-7 halftime lead.

"That's the longest of my career at any level," said McCluster. "What better time than that — Monday night football in Arrowhead. You couldn't ask for a better time."

Ryan Mathews, in his NFL debut, had 75 yards on 19 carries for the Chargers.

Rivers was 22 for 39 for 298 yards and two touchdowns. Matt Cassel, with a history of playing poorly against the Chargers, was 10 for 22 for 68 yards, including a 2-yard TD pass following a San Diego turnover.

The 9:15 p.m. kickoff was the latest in Arrowhead history.

"This was the longest day of my life," joked Cassel.

(This version CORRECTS Chiefs 21, Chargers 14. Corrects to 2 offensive TDs for Chiefs.)