By Steve Keating

KANSAS CITY, Missouri (Reuters) - The Kansas City Chiefs shocked the San Diego Chargers 21-14 on Monday to bring the curtain down on the opening weekend of the NFL season with a wet and wild upset.

Opening night featured plenty of fireworks and lightning but it was the Chiefs who provided a string of explosive big plays, highlighted by a club record 94-yard punt return from rookie Dexter McCluster that helped Kansas City to a 21-7 halftime lead.

Jamaal Charles also had the capacity crowd of 71,297 on its feet with a weaving 56-yard touchdown run, while Brandon Carr returned a fumble to the San Diego 12-yard line to set up a two-yard touchdown pass from Matt Cassel to Tony Moeaki.

The downpours dampened the party mood but it was also a major factor in the outcome, with the rain short-circuiting a Chargers attack late in the opening quarter.

"But that's alright, we're figuring out how you get things done.

"Our guys worked hard, they did a great job at preparation ... I thought they came out tonight and played their hearts out."

The Chargers dominated the early part of the game, Philip Rivers engineering a 60-yard scoring drive capped by a three-yard touchdown pass to Antonio Gates for a 7-0 lead.

Late in the third quarter with the stormy conditions subsiding, the Chargers finally answered with a big play of their own when Rivers hooked up with a wide open Legedu Naanee on a 59-yard touchdown to trim the Chiefs advantage to seven points.

The spectators who rode out the storm were left on the edge of their seats as Rivers worked the ball down to the Kansas City six with a minute remaining but could not find the end zone and the Chiefs were left to celebrate an unexpected win.

"They made some big plays," said Chargers' coach Norv Turner. "In terms of the weather conditions I thought they did good job handling that."

Rivers completed 22 of 39 passes for 298 yards and two touchdowns while Cassel connected on 10 of 22 attempts for just 68 yards and one touchdown. San Diego's total offence of 389 yards was almost double the Chiefs' 197 yards.

"Offensively we did what we needed to do to win the ball game," shrugged Cassel. "All in all we're really excited to get out of here with the victory.

"The conditions obviously had an impact.

"The offence didn't have a great night and a lot of that had to do with conditions but other aspects of the team, defense and special teams picked us up."

(Editing by Nick Mulvenney/Greg Stutchbury)