Through three games, the Eastern Conference finals have been all about LeBron James — for both good and bad. Whether it was his decision to pass up a potential game-tying shot in Game 1, or his failure to draw a foul at the end of Game 2, or his utter domination of Game 3, the King has been the lead story every night.

But at the end of it all, there’s a more surprising story that isn’t getting enough attention. For a second straight postseason, Detroit’s best player has hit a wall in the postseason and failed to get untracked in the conference finals, potentially leading to a second straight upset defeat. It comes as such a shock because this player has been synonymous with postseason success, winning the MVP award in the 2004 Finals and earning the nickname “Mr. Big Shot” for his exploits in the clutch.

But make no mistake, Chauncey Billups is struggling. Worse yet, he’s taking the entire Detroit offense down with him. Watching the Pistons this week, you’d have a hard time believing this was the league’s fifth-most efficient offense in the regular season (based on Offensive Efficiency, my measure of a team’s points per 100 possessions).

Heading into tonight’s Game 4 (8 p.m., TNT), Detroit’s offense has seemed positively Nets-like. They’re averaging 80 points a game, shooting 44.1% from the floor, and have yet to take more than 20 free throws in a game. They are up 2–1 this series thanks to equal parts defense and luck, but the fact remains that the Pistons are in far greater trouble than their lead in the series suggests.

Most of those problems point right back to Mr. Big Shot. On Sunday, for the third straight game, he finished with a meager 13 points and was bad enough in the first half that Pistons coach Flip Saunders sat him out nearly the entire second quarter.

Certainly, Cleveland’s defense has something to do with this. Billups is one of the league’s bigger point guards at 6-foot-3, 202 pounds, but the Cavs are one of the few teams that play even bigger and take away his size advantage. Cleveland has 6-foot-5-inch Larry Hughes guarding Billups and often brings in 6-foot-3-inch Eric Snow off the pine for backup.

But in the second half of Game 3, it wasn’t either of those two players guarding Billups. For the most part, it was a 6-foot-2-inch rookie named Daniel Gibson, the kind of chump Billups normally bullies on the blocks to earn multiple trips to the free-throw line. That he couldn’t do it speaks volumes to his recent funk.

Perhaps even more galling is the rash of turnovers from Billups. During the regular season, few were better at protecting the ball. Billups averaging 3.59 assists for every turnover, and his ability to play mistake-free basketball helped the Pistons to the league’s lowest turnover rate — just 13.5% of their possessions ended in a miscue.

The last three games have been a shocking departure from that pattern. Partly due to some clever traps sprung by the Cleveland defense, and partly because of a series of errant passes, Billups has turned the ball over 17 times in three games. Billups didn’t turn the ball over more than five times in a game all season, but in this series he’s had at least five in every game.

Thanks to Billups’s sudden error-proneness, Detroit’s precision offense has turned into the Larry Brown Knicks. The Pistons are turning the ball over on 19.2% of their possessions against Cleveland, and their 49 turnovers have helped create offense for a Cavs team that’s struggled mightily to generate clean looks in the halfcourt.

What has to really upset Detroit is that nearly the same thing happened a year ago. Then it was a second-round series against Cleveland, but the other factors were nearly identical — a 2–0 Pistons lead, a rally by Cleveland in Game 3, and Billups becoming suddenly unable to score. Detroit survived, barely, but Billups’s slump continued into the next series and Miami upset the Pistons.

For the 2006 postseason, Billups had the NBA’s third-largest decline in efficiency from the regular season (based on Player Efficiency Rating, my per-minute rating of a player’s statistical performance). He hasn’t been quite as bad this time around, but that’s mostly because he padded his numbers in Detroit’s first-round scrimmage against Orlando. Since the middle of the Chicago series, it’s been a rough ride.

I should point out that there are nine players sharing the court with Billups, and they’ve had an impact on the results as well. James, obviously, was amazing in Game 3, hitting two impossible jumpers in the final minutes and giving Cleveland the lead for good with an earth-shattering dunk on Rasheed Wallace. Plus, Billups isn’t the only struggling Piston — Richard Hamilton is 7-for-22 over the past two games and had only seven points in Game 3, for instance, while Tayshaun Prince is 7-for-32 in the series. Really, Rasheed Wallace is the only Detroit starter playing well.

But for me, it still goes back to Mr. Big Shot. He’s the best player on the team, and he’s the one that has to be punishing the Daniel Gibsons of the world in the low post or finding teammates for easy shots when the Cavs spring a trap on him as he passes halfcourt. As much criticism as James has taken for his failure to take the shot at the end of Game 1, it amazes me that Billups is getting a free pass for his inability to get Detroit’s offense in gear — especially since it’s the second straight postseason he’s failed to deliver the goods.

Perhaps this time it’s merely a short-term blip, the kind of minislump even great players experience from time to time. The Pistons better hope so, because Billups’s woes are undermining what was one of the league’s best offenses in the regular season.

Despite James’s brilliance (and headline-hogging), Cleveland is a clearly an inferior team — something a mediocre Nets team proved beyond any reasonable doubt a week ago. But unless Mr. Big Shot starts living up to his name, the Pistons are looking at an encore performance of last year’s conference finals disappointment.

jhollinger@nysun.com