SAN DIEGO – When Philip Rivers showed up in the Chargers’ weight room on Monday, his teammates noticed something different about his demeanor. He already was wearing his game face, proclaiming himself ready for the Patriots.

“I was thinking to myself, “We’ve got a long way to go. We’ve got six days to go, Philip,’ ” star running back LaDainian Tomlinson said. “He’s excited to be in his first playoff game. . . . We’ve got to remind him that a fast horse runs fast, but it doesn’t run long.”

Rivers’ behavior – and his performance – will be one of the keys in today’s AFC divisional playoff game at Qualcomm Stadium. The Chargers, coming off an opening-round bye, appear to be a Super Bowl-ready team, but they will head into the crucible of the postseason with a first-year starter at quarterback.

His lack of playoff experience is highlighted because of the quarterback on the visitors’ sideline – Tom Brady, who has three Super Bowl rings and an 11-1 postseason record. For Rivers, who acknowledged he hasn’t been in a playoff-type game since high school, this is like competing against Einstein at a science fair.

“I have no reservations whatsoever,” said Chargers coach Marty Schottenheimer, pointing to Rivers’ fourth-quarter statistics (a 116.6 passer rating) as evidence that he can handle pressure. After two seasons as Drew Brees’ understudy, Rivers ascended to the starting job and led the Chargers to a league-best 14-2 record. He encountered a couple of hiccups late in the season, but they never really affected the team because all he had to do was hand the ball to Tomlinson, the NFL’s MVP.

This is different. Rivers will be facing a defense known for its ability to dismantle quarterbacks, especially inexperienced ones.

Two years ago, then-rookie Ben Roethlisberger led the Steelers to 15 straight wins before imploding against the Patriots in the AFC Championship Game.

Presumably, the Patriots’ game plan will be to focus on Tomlinson, daring Rivers to beat them through the air. Rivers’ attitude? Bring it on.

“I would imagine that was the game plan of all 16 opponents,” he said.

Legends are made in January. In his playoff debut, after the 2001 season, Brady was nearly flawless in blizzard conditions, beating the Raiders. Asked how he felt going into that game, Brady replied, “Cold.” Maybe that explained the ice water in his veins. Now the pressure is on Rivers, whose sideline tantrum last month during a poor game against the Chiefs showed that emotions can get the best of him. Tomlinson, in a candid moment, admitted it’s a question.

“I’m not sure what to expect from him,” Tomlinson said. “He’s excited . . . but some part of being a quarterback, you keep that even keel of not getting too excited.”

(c) 2007, New York Daily News.

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