The Detroit Pistons are on a six game winning streak that has propelled them to the second best record in the Eastern Conference, and well en route to confounding expectations that the team was heading for a steep decline this season after a long run of success. That the Pistons are winning is a mild surprise, but how they are winning — with one of the top offenses in the league — is something of a shock.

It seems as if the Pistons have always been identified with defense since they moved from Fort Wayne in 1957, and for good reason. During their current run of excellence, five straight seasons of at least 50 wins, they have finished in the top five in Defensive Efficiency (points allowed per 100 possessions) four times and eighth the other time. The Bad Boys teams of the late ’80s and early ’90s won two titles with a defense-first strategy. Even shortlived bursts of glory like the Grant Hill teams of the late ’90s and the Dave Bing-Bob Lanier teams of the mid ’70s played stellar D. The implication couldn’t be clearer: When the Pistons play defense they win; when they don’t, it’s hello lottery.

Or at least that was the case until this season began. Minus the four-time Defensive Player of the Year, Ben Wallace, the Pistons have struggled to get stops and presently rank 26th in Defensive Efficiency — no that wasn’t a typo, I said 26th — allowing 104 points per 100 possessions. Only Washington, Seattle, Portland, and Milwaukee are worse at getting stops.

Even the Knicks rank higher than the Pistons, which tells you two things. For one, while Ben Wallace has yet to have the desired impact on his new team, the Chicago Bulls, his absence is sorely felt in Motown. And for another, that Pistons offense, which ranks second in the league in Offensive Efficiency, at 108.6 points scored per 100 possessions, is changing the public image of Detroit basketball.

The use of Efficiency metrics is crucial, as the Pistons play at one of the slowest paces in the league, averaging 91.6 possessions a game; only Portland and Jeff Van Gundy’s Houston Rockets play at a slower clip. Their pace depresses their points per game average, 98.4, which ranks 12th, well behind the league leading Denver Nuggets at 110.5, but the uptempo game played by the Nuggets results in an average of 13 more possessions a contest.

The change began last season when coach Flip Saunders installed a new offense. The big difference was that Saunders spread the floor. The team took substantially more three-point shots, 17.7 a game, five more than Larry Brown’s 2005 team that finished 16th in Offensive Efficiency. The new offensive design allows more room for some of the Pistons bread-and-butter plays, like the curl-in when guard Richard Hamilton comes off one or two screens, and is freed up for a mid range jump shot. Led by their newfound offense, which ranked third in Efficiency, and the ever stalwart defense, the Pistons cruised to 64 wins last year, only to stumble in the middle round of the playoffs when their long range marksmanship deserted them.

So far, it looks like the design of the offense has stayed largely the same, a shrewd judgment that what worked for six months shouldn’t be scrapped due to three bad weeks. Detroit is shooting 18 treys a game, and the slight offensive improvement may owe to replacing Wallace with Nazr Mohammed, an eight-year veteran and former Knick who has a nice touch on mid-range shots. Nazr is no match for Wallace defensively or in the hair department, but Big Ben was an offensive liability on the floor. The other key factor is that the Pistons are taking care of the basketball, they are the best in the league in percentage of possessions that result in turnovers.

The key to last year’s Detroit defense was that they didn’t foul anyone. The team forced you to play half court and if you beat your man on the perimeter, Wallace was there to protect the rim. This season, the team is allowing six more free throws per 100 field goal attempts. Also, the secure second line of defense allowed the Pistons to gamble in the passing lanes and force turnovers in bunches. This year, opponents are keeping the ball longer, the Pistons rank 22nd in forced turnovers, and it’s resulting in more scores.

Last season, the Pistons started out with a similar disparity between their offense and defense but by Christmas the defense had assumed its usual high ranking. If recent history is to repeat, Detroit will have to alter their blueprint or more often get volatile forward Rasheed Wallace to channel his inner Ben Wallace rather than his inner petulant child.

For now, the Pistons and their faithful can take solace in putting the ugly end to last year’s season behind them. This week’s slate is typical of their easy schedule so far: they play in Miami on Thursday and host the Knicks on Friday. Their fast start gives the impression that the Pistons can again take their place among the Eastern elite, but without defensive improvement this team is merely a threat to play until Memorial Day instead of late June. It’s a softer landing than many expected, but probably small solace for their fans who hoped this edition of the team would add another banner to the rafters of the Palace of Auburn Hills.

mjohnson@nysun.com