POWER RANKINGS: Defense pushes Mavs into top 15There is obviously a lot of noise with numbers around the 20-game mark, but the quick turnaround from finishing as one of the worst teams in the league to battling for a playoff spot is incredible to see. Can the Mavericks sustain this level of success?Let’s examine the four big reasons why the Mavs are rolling and determine what they could mean for the rest of the season…Luka Doncic isn’t just the future — he’s the present.The Slovenian wunderkind is blowing away expectations and looking like the Rookie of the Year favorite. He is averaging a team-high 18.5 points per game to go with 6.5 rebounds and 4.3 assists while shooting 44.3 percent from the field and 38.2 percent from 3-point range. He has displayed a variety of moves, fakes and shots, silencing any skeptics who anticipated his lack of speed and athleticism could limit his effectiveness. (As SB Nation’s Mike Prada notes, that might say more about evaluation methods than Doncic’s game.)Doncic scored 20 points in a highlight-filled win against the Rockets on Wednesday, draining contested 3-pointers and creatively attacking the rim. He may not possess the straight-line speed of a Russell Westbrook or John Wall, but he deftly uses hesitations and long finishing steps to work his way to the basket.Standing at 6-7, Doncic’s size not only allows him to get off shots smaller guards can’t attempt, but also creates better passing angles. This is a tough skip pass across the court, and Doncic puts it right on the money.There will always be struggles for rookies. Doncic is turning the ball over almost four times per game, and he is far from an All-NBA defender. It’s certainly possible his shooting percentages drop as he grinds through his first NBA season and opposing coaches throw new defensive challenges at him.But the Mavs found a true franchise cornerstone in Doncic. He is already the team’s top offensive option, and he will only improve with more experience.The Mavericks’ bench unit is a monster.Sure, Doncic deserves credit, but the bench mob has put it serious work to start the year.The starting unit has a plus-minus of minus-1.9, which ranks 23rd in the NBA. The bench, though, is at plus-3.8, No. 1 in the entire league by a considerable margin.Just check out what some of the reserves do on a per-100-possession basis:Mavericks BenchOff RatingDef RatingNet RatingMaxi Kleber112.897.415.4Dwight Powell113.3102.011.3J.J. Barea111.8102.79.1Devin Harris111.4103.08.4Barea in particular has been terrific, averaging 11.5 points and a team-high 5.9 assists in 20 minutes per game. He should receive a boost from playing with Dirk Nowitzki, his favorite pick-and-pop partner, once Nowitzki returns from injury. (Mavericks owner Mark Cuban told ESPN’s Tim MacMahon he could see Nowitzki back “within the next few weeks.”)The bench explosions are nice now, but relying on them to win games doesn’t seem like a sound long-term strategy. Rick Carlisle will have to push his starters to make more of an impact as the season progresses. They might not dominate on a nightly basis, but the first five guys can’t assume the bench will consistently dig them out of holes.Defense and rebounding matters.Dallas landed in the middle of the pack last season in terms of defensive rating, but the Mavs have jumped into the top 12 through their first 21 games.”We’ve gained an identity as a defensive team and that’s a really important thing for us,” Carlisle said Monday (via Mavs.com). “We are a defensive team first and we play off of our defense. The last two weeks we’ve picked up our defense to a very high level and the challenge is going to be to continue to keep it there.”The Mavericks are pushing opponents out of the paint, allowing the sixth-fewest restricted area attempts in the NBA. When a player does approach the basket, DeAndre Jordan is typically waiting to either block or alter the shot.However, the best rim protector on the team has been Kleber, who is keeping opponents around 50 percent at the rim, per NBA.com tracking data. That’s a number in line with bruisers like JaVale McGee, Hassan Whiteside, Aron Baynes and Joel Embiid.If a shot does reach the basket, the Mavs are corralling the rebound. Jordan is third in the league in rebounds (13.7 per game) and seventh in box outs (9.1 per game), but the team’s rebounding percentage doesn’t drop when he leaves the floor. Dallas is top three in defensive rebounding percentage (75.1) and top six in overall rebounding percentage (51.9). Though they likely won’t finish as one of the NBA’s elite defenses, the Mavericks can control how much effort they bring to that end of the floor each game. Simply maintaining energy and communication can make a huge difference. That defensive identity Carlisle mentioned will be key to a potential playoff berth. Through the first quarter of the 2018-19 NBA season, the best team in Texas is not the Rockets (11-11), the only contender that truly challenged the Warriors during their most recent title run. It is not the Spurs (11-12), a winning machine that has reached the playoffs for 21 straight seasons. No, the best team in the Lone Star State is the Mavericks (11-10), one of the biggest early surprises as the calendar flips into December. Dallas is nearly halfway to last season’s win total (24-58 overall in 2017-18) and currently sitting at No. 8 in a highly competitive Western Conference. A little luck doesn’t hurt.The Mavs have taken advantage of injury troubles to top teams in adding to their win total. They missed star matchups with the Rockets’ Chris Paul, Thunder’s Russell Westbrook and Warriors’ Stephen Curry and Draymond Green. They also caught the Celtics on a back-to-back. That’s four of their 11 wins right there.Dallas has enjoyed the fifth-easiest strength of schedule so far, but that will be changing soon. The Mavericks hold the second-toughest remaining strength of schedule in the league, according to Tankathon, with multiple matchups left against the Warriors, Bucks and Clippers.The play as of late is undoubtedly encouraging. However, the Mavericks’ biggest tests lie ahead and will determine whether this team is the real deal or an early-season anomaly.