Come back, Nelly. All is forgiven. If the Mavericks are echoing that sentiment right now, it’s because they have good reason to. For the first time since taking over from legendary tinkerer Don Nelson in March, Dallas’s rookie coach, Avery Johnson, is looking like, well, a rookie coach.

As a result, the Mavericks find themselves trailing the Houston Rockets 2-0 in their first-round playoff series. Having lost both contests at home, Dallas now must win twice on the road to regain its home-court advantage.

It wasn’t supposed to be this way. Dallas looked every bit the playoff sleeper after a season-ending 16-2 spurt under the Little General. With Johnson’s emphasis on defense, the Mavs redoubled their efforts at that end of the floor while their dominant offense remained potent. Thanks to its closing thrust, Dallas finished with 58 wins and nearly wrested the Midwest Division crown away from the San Antonio Spurs.

Yet in the first two playoff games, that vaunted defense has been glaringly absent. In Game 2, Houston shredded the Mavs with 54.8% shooting. Yao Ming was especially lethal, making 13-of-14 shots. In the process, he made a mockery of Dallas’s Erick Dampier’s claim that he, not Yao, was the West’s best center.

Dallas’s unexpected postseason struggles have cast a harsh light on Johnson’s decisions. In Game 1, the Mavs were so sluggish that a Phil Jackson-Red Auerbach hybrid couldn’t have coaxed them to victory. Of course, that lethargy may have been partly Johnson’s doing; while the Rockets were resting up for Game 1, Johnson had his team practicing hard on both off-days.

“We looked like we were running in sand,” Johnson said after the Game 1 defeat. You don’t say.

Seemingly intent on giving his critics more material, Johnson unleashed a post game tirade directed at referee Joey Crawford. That didn’t reassure anyone that he had things under control, especially since he had to be restrained from escalating things further.

A bigger faux pas came in Game 2. With the Mavs showing much more energy than they had in the opener, the contest was Dallas’s for the taking – but Johnson opted not to take it.

A little background information is in order first. At various times this year when the Mavs played against a big, slow center, they went with “smallball” lineups to outrun opponents and were hugely effective. Centers don’t get any bigger and slower than Yao, yet the Mavs tried to play “straight” in the opener and got schooled.

Dallas’s game plan for the second contest seemed obvious: Go small and try to take Yao out of the game. Accordingly, Johnson unleashed the small lineup in the second quarter – removing Dampier and playing Josh Howard at power forward and Dirk Nowitzki at center. It worked like a charm.

Since having Yao guard Nowitzki would be suicidal, the Rockets tried unsuccessfully to put him on Howard. The Mavs’ forward repeatedly drove past Yao, scoring four baskets in three minutes. Howard also drew a foul on Yao, who became exhausted from chasing a smaller player around the perimeter.

That should have set the stage for the second half. Most observers guessed that Johnson, having seen how effective smallball was in the second quarter, would start his smallball lineup to begin the half. Doing so was of huge importance because Yao was absolutely destroying Dallas at the other end. But Johnson started the half with his regular lineup…and stuck with it. The Mavs’ most effective weapon was sidelined when it was needed most.

While Johnson is taking his share of criticism, a few other Mavs deserve their share, too. Dampier’s boasting would be more believable if he weren’t getting lit up like Times Square by Yao, who has 44 points in 56 minutes in this series. Moreover, Dallas’s alleged bench advantage has failed to materialize. Houston’s reserves outscored the Mavs’ subs in both games, as Jon Barry and Mike James have proven far more accurate than Jerry Stackhouse and Keith Van Horn.

Then there’s Dirk Nowitzki. The Mavs’ superstar had an MVP-caliber season this year, ranking behind only Kevin Garnett and Shaquille O’Neal in my estimation. But you’d never know that from the first two games. In the opener, Nowitzki seemed half-asleep. Despite a matchup against Ryan Bowen that practically begged for him to dominate, Nowitzki shot just 5-for-19 and committed six turnovers. He wasn’t much better in the second game, going 8-for-21. The normally laser-accurate German is shooting a measly 32.5% in the series and has as many turnovers (9) as rebounds.

In fairness, I should point out that the Rockets aren’t exactly chopped liver. Houston won 51 games in the regular season, which is more impressive when you consider they started 12-14. In the second half, the Rockets were 29-12, a 58-win pace for a full season – which matches Dallas’s total.

One Rocket in particular has been spectacular. Tracy McGrady’s game winning shot on Monday night wrapped up an epic effort that included 28 points, 10 assists, eight rebounds, three blocks, three steals, and one poster-quality dunk over Shawn Bradley. And one could argue that he was even better in the opener.

But regardless of the Rockets’ exploits, the cold facts remain: The Mavs were favored and riding a hot streak but managed to lose the first two games at home. All eyes are on the rookie coach to see what he has cooked up for Game 3.The small ball lineup certainly should play a part – in fact, he should start the game with it now that he’s got nothing to lose. He also should consider finding more minutes for reserve Marquis Daniels, a talented wing player who has been a bystander the first two games. A little pep talk with Dirk wouldn’t hurt, either.

The big test comes tonight. This is why Mark Cuban is paying Johnson the big bucks. Everything seemed fun and easy when the Mavs were winning, but ultimately, coaches are judged by what they can do to snap their team out of a rut. If tonight’s Game 3 doesn’t turn out differently from the first two, the same fickle folks who were calling for Nelly’s head two months ago might instead ask for Johnson’s.