DALLAS — Dirk Nowitzki's one-game suspension last night gave the Mavericks a perfectly good excuse to fall apart against Houston.

They readily accepted.

This is all you need to know: Josh Howard was the Mavs' only starter on the court with four minutes left in the game.

Houston 113, Dallas 98.

Can you say embarrassment?

The Mavs, losers of four of their last five games, trailed by 17 points after three quarters to the red-hot Rockets, who won their 17th consecutive game.

The Mavs are supposed to be better than that.

Maybe they're not. Maybe it's time for all of us to accept that. Maybe, it's time for us to lower the standard by which we judge them.

The reason: This team simply isn't mentally tough enough.

It tends to crumple under adversity, which is what happened against the Rockets.

We've rightfully questioned the Mavs' mental toughness since their debacle in the NBA Finals against Miami.

Two seasons later, the same questions remain.

Without Nowitzki in the lineup, courtesy of a horse-collar tackle against Utah, Jason Kidd, Jason Terry and Howard each had an opportunity to put the team on his back and lead it to victory.

None of them did.

Meanwhile, Rafer Alston and Tracy McGrady had their way with the Mavs, who lacked energy and played without passion for much of the night.

The Mavericks trailed by two points at halftime but never had control of the game. Houston always seemed on the verge of blowing out Dallas, and in the third quarter, the Rockets fulfilled their destiny.

The Mavs have an opportunity to erase the doubts surrounding their ability to compete for a championship this season during this 10-game stretch that began against Houston.

Realistically, the Mavs need to win eight or nine games during this stretch to make a move in the Western Conference. Losing the first game makes that task more difficult.

After all, this team has not shown an ability to string together wins — even when playing bad teams.

You may not want to deal with this, but the Mavs are a lot closer to missing the playoffs than they are to the No. 1 seed in the Western Conference.

We continue to assume the Mavs will make the playoffs, and there's still no reason to panic, but a team this mentally fragile will lose its confidence quickly. Then it might really plummet.

Hey, we've seen it before.

The Mavs still have not beaten a quality team since the Jason Kidd trade, going 0-5 against teams over .500. It's not enough to play well against the best teams in the Western Conference.

At some point, if the Mavs are an elite team, they have to win some of those games.

Dallas has one victory over a team with a winning record since Feb. 4 — a 96-76 victory over Portland — a span of 14 games.

Ridiculous.

The Mavs are 14-19 on the road, an indication that they can't handle adversity.

Again, ridiculous.

And they are only 13-11 against the raggedy Eastern Conference.

Say it one more time, ridiculous.

We can all agree mental toughness is an ambiguous term that encompasses a lot of the intangibles in sports. This much is true: You know it when you see it.

At least Johnson does.

When he talks about mental toughness, he's talking about players maintaining their composure during the inevitable ebb and flow of an NBA game. He's talking about "dirty" rebounds, the kind where one player fights harder for the ball than his opponent.

He's talking about putting teams away when the Mavs have a big lead in the fourth quarter so the regulars can rest, and he's talking about guys who consistently play through the pain that accompanies an 82-game season.

The Mavs have players who will do all of those things. They just don't do it consistently.

That's a big problem.

These Mavs are still searching to find themselves after the trade that brought Kidd to town.

It just hasn't happened yet.

There's still time for the Mavs to find their way. Three weeks to be exact.

But it's never going to happen without some intestinal fortitude.