Before Tuesday night, the Dallas Mavericks held the interesting distinction of being the only playoff team that hadn’t been run out of the building in a playoff game. The Mavs’ four losses had come by margins of one, two, three, and five points.

Then came Tuesday’s 106-86 Game 4 plastering at the hands of the Phoenix Suns, a game whose victory margin could easily have breached 30 points had Phoenix not slammed on the brakes late in the fourth quarter. Dallas simply gave up with six minutes to go, down 18.

That Mavericks coach Avery Johnson threw in the towel at that point was notable because his team had rallied from just such a deficit in Phoenix on opening night of the regular season. In that game, his troops found themselves avalanched under a barrage of Suns 3-pointers. But they held firm, tightened up the defense, and set forward Dirk Nowitzki loose from behind the arc. The next thing you knew, the game was heading to overtime and Dallas eventually prevailed.

Tuesday night’s Mavericks bore little resemblance to the opening night crew in terms of mettle and toughness, so Johnson decided to go back to the drawing board. He’ll need to, because while the Mavericks are still the deeper and more talented team in this series, the Suns exposed several weaknesses that Johnson must address quickly.

First off, the Suns caught on to something that Dallas’s other main rival, the San Antonio Spurs, have known for years: When the Mavericks get rattled, a little physical play can push them into submission. Toward the middle of Phoenix’s second-half run of Game 4 that transformed a tight 67-65 contest into a 91-67 blowout, Suns guard Steve Nash pulled Nowitzki down during a scrum for a rebound. A little later, Suns forward Tim Thomas smacked Mavs guard Jason Terry in the head while pursuing a loose ball. Finally, guard Raja Bell, whose return from a torn calf muscle gave the Suns a great emotional lift, submarined Nowitzki, sending both players to the floor in a heap.

The Mavs complained vociferously, picking up technical fouls in the process, and thanks to the gratuitous but hardly misdemeanor-level contact, they completely lost their focus on the game.

Then again, it’s fair to wonder how much the Mavs ever really focused on this contest. Nowitzki led a parade of Dallas bricklayers, shooting only 3-of-13. Terry went 4-of-11 and swingman Jerry Stackhouse went 4-of-10, which is worse than it looks because he missed several short, open looks.

The Mavs’ coaching staff appeared to have mistaken the contest for a regular season game, failing to make significant adjustments to the tactics they used in their Game 2 and 3 wins, and seemed flustered when the Suns altered their offense.

In winning Games 2 and 3, the Mavericks employed rangy young pivotman DeSagana Diop as an intimidator in the paint. It worked. The Suns were denied easy shots and their lightning quick offense slowed to a crawl.

In Game 5, Phoenix responded by spreading the floor further, with Nash sometimes backed all the way to the center court jump-ball circle to start the offensive sets. The extra stretch pushed Dallas’s defense past its limits. When the double teams came at Nash, the Suns were able to rotate the ball effectively to an open shooter spotting up along the 3-point arc.

Johnson and his staff seemed surprised that the Suns would alter their tactics, but they failed to find any in-game counter. One of Dallas’s great strengths has been its play in the second halves of games, a testament to the in-game adjustments by the coaching staff. In Game 4, the staff mailed it in, too.

Although the Suns showed considerable spunk and ability in winning Game 4 and knotting the series at two games apiece, their momentum is limited going into tonight’s Game 5. For starters, there remain questions about how much Bell will be able to play. It looked as if he aggravated the calf injury during the fourth quarter, and his absence deflated the Suns defense in Games 2 and 3. Secondly, Nowitzki and company are unlikely to repeat their wretched shooting back at home in Dallas.

Two keys to consider are turnovers and rebounding. In Game 3, the Mavericks committed only five turnovers, a number they were highly unlikely to repeat – and they didn’t, throwing the ball away 14 times the following game. Phoenix – high-risk offense and all – only turned the ball over seven times in Game 4, a number that is likely to double tonight. Also, Nowitzki has not only keyed the Dallas offense, but his rebounding -14.3 per game in the series – has keyed the Dallas defense. He had only seven boards on Tuesday night, so look for him to re-assert himself inside.

With two of the remaining three games in Dallas, the Mavericks remain the favorites to win the series. But in letting their guard down and letting Phoenix back into the series in Game 4, they showed they still have some work to do on their championship mettle. The Mavs’ conquering of San Antonio in the second round was a big step forward for the franchise, but they still have a ways to go before they get the respect they want.

mjohnson@nysun.com