KANSAS CITY, Mo. -- Tough and gruff Todd Haley took his young playmaker into his arms and put his mouth to his helmet. With the renovated New Arrowhead Stadium crowd going berserk, Haley screamed into Dexter McCluster’s ear hole.

“He said, ‘Keep making plays,’" McCluster said after making the signature play in a stunning 21-14 Kansas City upset win over four-time defending AFC West champion San Diego in one of the most exciting nights in recent Chiefs history. “It’s great for a coach and a player to celebrate together. It was a special moment.”

After dropping the tiny McCluster to the turf following the rookie's team-record 94-yard punt return in a driving rain storm, giving the Chiefs a 21-7 lead, Haley pumped his fists in ecstasy.

“This is how I envisioned Arrowhead,” Haley said. “Usually the team that plays the best wins in the end and we played the best.”

It was a night of celebration in Kansas City as the Chiefs made big plays, watched their rookies come up big and witnessed their young defense make a huge defensive stand in the final seconds to deny the roaring Chargers.

The Chiefs, who long ago requested to open the season on Monday night, unveiled the New Arrowhead Stadium in style. Perhaps the grand old house inspired this young 2010 version of the Chiefs to play like some of the great teams of Kansas City’s past.

This game was clearly the highlight of the 20-month-old Scott Pioli-Haley era. The Chiefs had won a total of 10 games in the previous three seasons.

As a reward for their first opening-weekend win in five years, Kansas City is now in sole possession of first place in the AFC West for the first time since Week 7 of the 2007 season, according to ESPN’s Stats and Information.

Heading into the regular season, it seemed like it would be San Diego and everyone else in the AFC West. If one week is any indication, the Chiefs must be accounted for. Not only were the Chiefs the only team in the division to win, but they were the only team to show significant improvement in Week 1.

Oakland, which has high hopes for resurgence, was blasted by 25 points in Tennessee, and Denver looks like a work in progress after a loss to Jacksonville. The Chargers had their moments and their chances Monday night.

San Diego was clearly affected the rain and wind, which dominated the second and third quarters before subsiding in the fourth quarter. The Chargers, who had one first down in a 30-minute, 14-second span, tried to come back late, but the Chiefs would not be denied on this special night

“Monday Night Football and a big win,” No. 5 overall pick Eric Berry said. “It was great.”

Berry was part of the Chiefs’ last stand. Clearly relieved by the end of the rain, the Chargers came hard at Kansas City and were poised to tie the game and send it to overtime.

The magical night was in peril when San Diego quarterback Philip Rivers completed a 12-yard pass to receiver Legedu Naanee to the 4-yard line with 1:14 remaining. It came on fourth-and-3. Yet, Kansas City’s defense did not crumble. Rivers threw two incompletions and running back Darren Sproles was stopped for a 2-yard loss. On fourth down-and-goal from the 6 with 39 seconds to go, Rivers couldn’t connect with receiver Malcom Floyd in the back of the end zone.

The water-logged Arrowhead crowd, which was boisterous all night, erupted as it saw K.C.'s defense come of age.

“They played every play,” Haley said. “That is one of our little mottos: 'Play every play.' And they did.”

If Kansas City’s defense plays this well on a consistent basis, the Chiefs will be candidates for a winning season. The defense often abandoned Kansas City last year. Other than new coordinator Romeo Crennel and Berry, there are few new additions.

But players such as defensive lineman Glenn Dorsey (who may have played his best NFL game after being the No. 5 overall pick in 2008), revived linebacker Derrick Johnson and third-year cornerback Brandon Carr all led the charge. Dorsey harassed Rivers on the final play.

Kansas City, led by a wicked 56-yard touchdown run by dynamic running back Jamaal Charles and big special-teams plays by McCluster and fellow second-round pick Javier Arenas, will score its share of points. If the defense is this stout, Haley will end up doing a lot more celebrating with his players.

“It’s a good start,” a smiling Haley said. That’s what Monday night was all about in Kansas City -- a new beginning.