Check out this weeks NBA power rankings Get Expert NBA Picks by clicking each of the handicapper pages under the "Advisory Board" section of the left side bar.

Tis' the season for pre-Christmas NBA coaching casualties, and we're already at six and counting. Some, such as Minnesota's Randy Wittman and Eddie Jordan of Washington, came as no surprise.

But others were a little perplexing. Maurice Cheeks wasn't given a chance to see the 76ers through their early struggles and the same went for Sacramento's Reggie Theus, who might have deserved a little slack given the fact that he took one of the league's least talented teams last year and nearly finished .500. So it goes in the ever-fickle league.

Here are the NBA Power Rankings through Dec. 21:

1. Boston Celtics (26-2) - With a franchise-record 18-straight wins, can there possibly be any argument here? The good news for the gamblers is that the Celtics also have cashed in seven of their past 10 outings.

2. Cleveland Cavaliers (23-4) - A little bit overlooked amid the deserved attention Boston is getting for its historic run is the fact that the Cavaliers haven't slowed down much, either. They have won nine of 10 straight up, covering in eight and continuing their own record start.

3. Los Angeles Lakers (21-5) - The league's highest-scoring team has been a bust at the cashier's cage of late. Despite winning seven of their last 10, the Lakers have failed to cover in nine straight. Such is the price of a prolific, popular team; eight of those nine spread have been in double digits.

4. Orlando Magic (21-6) - The Magic have been on fire on the hardwood and at the sportsbook, covering in seven straight while also winning four of five on a tough recent road trip. The lone defeat was by one point. They have won eight of their last 10 overall.

5. Houston Rockets (18-9) - The up-and-down Rockets are up again, for the moment. They have won seven of their last 10 and, what's more, Yao Ming and Tracy McGrady have managed to make it a week without a trip to the disabled list.

6. New Orleans Hornets (16-7) - After a bit of a sluggish start, the Hornets are starting to look like the breakout team they resembled last year. They have won eight of 10 and covered in six of those. Upcoming home games against the Lakers and Rockets should provide a true sign of their progress.

7. Denver Nuggets (17-10) - The Nuggets' recent momentum hit a snag, with three straight losses after a four-game win streak. They have failed to cover in four of their past six.

8. Portland Trailblazers (17-10) - The Trailblazers finally have found in Brandon Roy what they have long needed; a superstar who can come through in the clutch. His 50-point outing in last week's overtime win over the Suns is proof that Roy is capable of taking Portland from also-ran to contender.

9. San Antonio Spurs (16-10) - The Spurs followed a six-game winning streak by losing two of their past three. They have slowed down at the cashier's cage as well, failing to cover in four straight.

10. Atlanta Hawks (17-10) - The Hawks could have used a win over Boston to further their early-season momentum; however, they are still 5-1 straight up and ATS in their last six outings.

11. Utah Jazz (17-12) - The Jazz have struggled mightily with the injury bug, and likely will be inconsistent until they are at full strength. The loss of Carlos Boozer indefinitely won't help their cause. Even so, the Jazz have managed to cover in three of their past four games.

12. Dallas Mavericks (15-11) - The Mavericks continue to improve under Rick Carlisle, but they are hardly the high-scoring Mavericks of old, 13th in the league at 100.2 points per game. They have won seven of 10 but covered in just three of those games.

13. Phoenix Suns (16-11) - Analyst Jeff Van Gundy had it right when assessing the Suns' lack of defense: "They get paid enough to try hard on both ends." But apparently big money isn't enough motivation. Phoenix ranks 25th in total defense, which helps explain its 11-16 ATS mark.

14. Detroit Pistons (14-11) - The Pistons have struggled since the Chauncey Billups trade and have been erratic at best. Losses in six of their last 10, including to clubs such as New York and Washington, aren't a good sign for this perennial contender.

15. Miami Heat (14-12) - The Heat bounced back from a three-game losing streak with impressive wins over the Lakers and the Nets, breaking a six-game losing streak ATS in the process.

16. New Jersey Nets (13-13) -At least the Nets are consistent; when they happen to win, they usually cover. Young point guard Devin Harris has carried this otherwise weak roster. They have won and covered four of their past 10 games.

17. Chicago Bulls (13-14) - Lack of a post presence really hurts this team against the league's better clubs or, for that matter, the mediocre ones as well. The Bulls have split their past 10 games but covered just three times in that span.

18. Milwaukee Bucks (13-16) - It might be another year before this team turns the corner, but the Bucks have shown plenty of promise. This is reflected in their 19-9-1 mark ATS, as well as winning and covering four of their past five.

19. New York Knicks (11-16) - The league's second-worst defensive club - a Mike D'Antoni staple - has suffered seven losses in its past 10 games but has also managed to cover in seven of its last 10.

20. Philadelphia 76ers (12-15) - The coaching change was a brief wake-up call for the 76ers, who have won and covered in three of their past four but got some bad fortune when Elton Brand was lost to injury for the next month.

21. Indiana Pacers (10-17) - The Pacers have rebounded from six straight losses to win three of four, but two of those came against the Warriors and 76ers.

22. Toronto Raptors (10-17) - The Raptors have been mired in an offensive funk, failing to score more than 97 in any of their past five games. No surprise, each was a loss and there's no money in the hands of bettors.

23. Charlotte Bobcats (9-19) - Like a movie that continues to get bad reviews but somehow thrives at the box office, the Bobcats are 16-12 ATS despite losses in eight of their last 10 games, which included a seven-game losing streak.

24. Memphis Grizzlies (9-17) - Being on the Grizzlies is like showing up at a rec league game where a team is short players. If you're in the gym, you're going to play. But the rag-tag Grizzlies are on a mini-tear, going 4-1-1 ATS and 4-2 straight up in their last six.

25. Los Angeles Clippers (8-19) - The Clippers quietly have assembled a respectable frontcourt in Zach Randolph, Marcus Camby and Chris Kaman. Their record is better for it, too; they have won and covered in four of their past six games.

26. Golden State Warriors (8-20) - By far the league's biggest disappointment thus far, the Warriors are further depleted by an injury to Steven Jackson. They have dropped five of their last six overall and ATS.

27. Sacramento Kings (7-21) -This team is just too thin talent-wise to expect much from. The good news is, they get 10 or more points frequently and have covered four straight double-figure spreads.

28. Minnesota Timberwolves (4-22) - Betting on the T'Wolves is like getting an elbow to the nose from Kevin McHale on one of his up-and-unders: it hurts. They have lost 12 straight and have only three cashes during the streak.

29. Washington Wizards (4-21) - Things aren't looking much brighter for the Wizards, who haven't sniffed a win or a cover in nearly two weeks, going 0-6 in both regards during this time.

30. Oklahoma City Thunder (3-25) - The Thunder like to do things in bunches. During their recent nine-game losing streak, they managed to cover five times and have covered four more in their last five.