When the Dallas Mavericks opened their season on Christmas Day against the Miami Heat, they had a starting line-up of Jason Kidd (38), Vince Carter (35), Shawn Marion (33), Dirk Nowitzki (33) and Brendan Haywood (32). The first two players off the bench were Jason Terry (34) and Lamar Odom (32).

When they won an NBA championship last season with a similarly ancient roster, they had Tyson Chandler, an athletic 7’1, 235 Second-Team All-Defensive center protecting the paint. Without him, as well as perimeter stopper DeShawn Stevenson, Dallas’ defensive rating has slipped from 8th to 19th this season.

Haywood doesn’t have Chandler’s agility or athleticism; his 16.5% rebound rate this year lags behind Chandler’s 19.7% mark last season. With both Nowitzki and Marion’s rebound rate slipping with age, the Mavericks are averaging only 37.0 rebounds a game, 27th in the NBA, despite playing at the league’s 8th fastest pace.

At 7’1, 260 with a 7’6 wingspan, Haywood is still a valuable post defender, but he’s a bad fit for a team that allows so much dribble penetration. The Mavericks have significantly lower team defensive ratings with his two younger and more athletic back-ups -- Ian Mahinmi (26) and Sean Williams (25) -- in the game.

The good news for Dallas is that Rick Carlisle is one of the most flexible coaches in the NBA. After consecutive blow-outs to the Heat and the Denver Nuggets, two athletic teams who push the pace and attack the basket, he abandoned the idea of rotating Haywood, Nowitzki and Odom at the center position.

But while both Mahnimi and Williams are comparable athletically to Chandler, they aren’t as big as he was and they can’t replace his offensive rebounding, 73% free-throw shooting or ability to stay out of foul trouble. When the Mavericks let Chandler walk in free agency, they were abandoning any realistic chance of repeating as champions.

However, they aren’t nearly as bad as their 2-4 record and their -4.3 point differential suggests.

The acquisition of Delonte West, an athletic 6’3, 200 combo guard with a 6’6 wingspan, was one of the most underrated moves of the off-season. For a Mavericks team lacking a perimeter stopper with Stevenson in Washington, West is invaluable, especially with the aging trio of Kidd, Carter and Terry getting so many minutes.

All three are still valuable NBA players, extremely skilled veterans who can stretch the floor and make plays for their teammates. But at this point in their careers, their games replicate more than complement each other. None of the three have the athletic ability to consistently drive to the rim, with 21% of Carter’s shots, 5% (!) of Terry’s and 0% (!!) of Kidd’s coming in the lane this season.

The departed JJ Barea, now in Minnesota, took 31% of his shots in the paint. Inserting the diminutive guard into the starting line-up helped swing the tide of the 2011 NBA Finals not because his stature inspired his teammates or demoralized his opponents, but because he could attack the basket with the driving lanes Dirk’s outside shooting created.

When you have a seven-footer capable of dragging opposing power forwards all the way out to the three-point line, it’s practically negligent to not to play a guard who can take advantage of all the extra space on the interior.

As the season goes on, Carlisle will have to increase West’s role offensively, as the 28-year-old takes 36% of his shots in the paint. Another option off the bench is third-year guard Rodrigue Beaubois, a 6’2, 180 blur with a 6’9 wingspan who took 37% of his shots in the lane as a rookie and 28% last season.

Meanwhile, Dallas’ most high-profile off-season acquisition, Lamar Odom, has struggled with his new role. With an athletic shot-blocker at center a necessity and Nowitzki firmly entrenched at the four, Odom has played a lot of minutes at small forward, taking 2.8 three-pointers a game despite shooting 17.6% from beyond the arc.

But his three-point percentage should improve as he gets in better shape, and as a small forward, he can use his size differential to play more out of the post instead of from the perimeter, which he is what he did as a power forward with the Lakers next to Pau Gasol. It will take a defensive juggling act to keep Odom and Nowitzki on the floor at the same time, making Marion and Mahinmi’s positional versatility more valuable, but Carlisle has shown the ability to deploy creative zone defenses in the past.

The Mavericks can rotate three players at center to provide interior defense behind a three-man forward rotation of Nowitzki, Marion and Odom. And with such a compressed schedule, there should be ample minutes on the perimeter for West and Beaubois next to Terry, Carter and Kidd, three of the oldest guards in the NBA.

It’s a rotation with a lot of moving parts that won’t become cohesive over night, one probably not good enough to defend their 2011 championship. But it’s a lot better than the group that was embarrassed on Christmas Day and it should be enough to keep Dallas competitive among the large group of teams in the West jockeying for playoff positioning behind the Oklahoma City Thunder.