The NBA saw two big surprises on Christmas Eve. For starters, it had the first coaching change of the new NBA season. Next, the guy who lost his job wasn’t named Isiah.

Instead, it was the Chicago Bulls who were first to change skippers after a horrific 9–16 start in which they performed the difficult feat of losing to both the Knicks and the Nets. Expected by some prognosticators to win the East (pardon me while I don a trenchcoat and sunglasses), the Bulls instead found themselves 13th in the Eastern pecking order, with only the pathetic Knicks having a worse scoring margin.

The turnaround was so shocking because the Bulls made no major changes to last year’s squad — one that won 49 games and had the victory margin of a 57-win team. Moreover, Scott Skiles had been the driving force behind an overachieving, hustling squad that led the league in Defensive Efficiency (my measure of a team’s points allowed per 100 opponent possessions).

Yet somewhere over the summer, that passion seemed to vanish. Chicago is just 10th in Defensive Efficiency this season, which is good, but not nearly good enough to overcome their offensive deficiencies. And those weaknesses mushroomed this year, as guards Kirk Hinrich and Ben Gordon have been in mysterious funks all season — entering last night’s game in San Antonio they were shooting 38.0% and 38.5%, respectively.

The irony here is that both the Bulls general manager, John Paxson, and the man he fired, Skiles, share the same weakness — they stayed the course for far too long. Paxson inexplicably passed on a chance to trade for Memphis’s dynamic power forward Pau Gasol last season, which would have given the Bulls the low-post offensive force they’ve been craving. As it turns out, he may have blown his only shot at winning the East through his inaction.

Skiles had a similar problem this year — when it became obvious early on that the Bulls were a far cry from the club that fared so well a year ago, he just kept trotting out the same lineups. High-scoring forward Andres Nocioni stayed on the bench despite the team’s readily apparent need for scoring, while free agent bust Ben Wallace kept getting minutes in the middle in spite of his clearly diminished impact at both ends of the floor.

So the coaching shift is the first change, but it can’t be the only one. The Bulls are likely to hire Skiles’s lieutenant Jim Boylan as the interim coach for the rest of the season — he didn’t travel with the team to San Antonio so he could stay in Chicago and work out terms with Paxson. But he’ll have to make some radical departures in his personnel usage, because what Skiles did wasn’t working.

I’d recommend benching vets Wallace and Joe Smith, and instead starting Nocioni and rookie Joakim Noah in the frontcourt, while using Tyrus Thomas as the primary frontcourt sub off the bench. They’d have to play smaller and faster and let the chips fall where they may, but that might be the necessary step for the team to rediscover the scrapping, feisty attitude that made them contenders in the first place.

As for Paxson, my own rule of thumb is that a GM is on the hot seat from the moment he fires a coach who he hired. That certainly applies in this case. Not only did Paxson err with his inaction on Gasol last February, he overpaid Wallace in the summer of 2006 and compounded the error by letting two other talents — Tyson Chandler and J.R. Smith — slip through his mitts in trades with New Orleans and Denver, respectively.

Paxson will jump into the market for coaching talent this offseason, but in the meantime he has to look more seriously at trades to reshape the league’s worst offense into more of a threat. I know what your first thought is, but forget it — if Kobe Bryant doesn’t like playing for the 18–10 Lakers, how’d he like playing for these guys?

Instead, Paxson has to more seriously explore a Gasol deal with Memphis, find out what the market is for his name players, and convince Boylan to find some minutes for the young guys so the Bulls can figure out what they have heading into 2008–09.

That’s right: They need to start thinking about next year. Don’t get me wrong — the season is still early enough, and the bottom of the East bad enough, that it’s very easy to imagine the Bulls wedging their way into one of the conference’s final playoff spots. But with the top of the East stronger than it has been in ages and the Bulls taking a gigantic step backward, Chicago has to acknowledge its new standing in the pecking order. Monday’s coaching change was the first step.

jhollinger@nysun.com