DALLAS — Why would an opposing NBA team use anything other than a zone defense against the 76ers?

It was their kryptonite during Brett Brown’s tenure as coach and they’ve have had problems adjusting to it in two seasons under Doc Rivers.

At times, the Sixers have looked like fifth-graders taking a surprise Calculus I exam. They were tested again in Friday night’s 107-98 loss to the Dallas Mavericks at American Airlines Center. And failed miserably. The Sixers struggled mightily after the Mavs (30-23) went to a zone soon after intermission.

The Sixers went from shooting 46.2% from three-point land in the first half to making just 3 of 14 threes (21.4%) in the second. They were also held to 15 and 20 points in the third and fourth quarters, respectively, after scoring 63 points in the opening half.

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“We’ve got to figure some stuff out,” Seth Curry said. “It’s been a few times this year we’ve been pretty bad against the zone.

“It’s like if we don’t get Joel [Embiid] in the middle of the paint, the front of the rim, we rarely get a good shot. So we have to figure out some other options out of that zone, find ways to attack.”

Curry believes if the Sixers (31-21) can make two or three good plays, teams will be forced to come out of the zone. But so far, facing a zone for several possessions has been tough for the Sixers.

“We’re not executing,” Curry said. “We don’t really know what to get into. And if guys are not getting good shots, it makes it tough.

“It’s similar to a team playing good defense, but good coverage that we’re trying to figure out.”

The Sixers must view game film and figure out an offense to run against such a scheme. They know the zone is something teams have utilized to get them out of their groove. And after Dallas’ success, they’re definitely going to see it again.

“So we have to figure it out,” Curry said.

One can only expect the Chicago Bulls, at some point, to use the defensive tactic Sunday against the Sixers at the United Center, if they can’t stop Embiid.

The bottom line is when it counts, teams will drop into a zone against them. That will be a major case of concern in the playoffs.

In addition to not knocking down shots, the Sixers did a poor job of penetrating the Mavs’ zone. Having ball handlers drive to the paint would have opened things up. The ball handler could have gotten to preferred spots on the floor or kicked the ball out to shooters. But even that wouldn’t have mattered without the Sixers knocking down three-pointers.

Like Curry said, one of the best ways to get teams out of a zone is to knock down perimeter shots. However, the Sixers ranked 28th out of the league’s 30 teams in three-point attempts (31 per game).

On Friday, they attempted 27 threes, making nine of them (33%).

“We didn’t take the wide-open shots that we should have,” Embiid said. “The ball didn’t move the way it should have been moved. And then we didn’t attack. We kept settling, passing the ball around the three-point line. But we never actually got to the paint.”

Embiid has been saying he wanted his teammates to attempt more three-pointers all season. He thinks the Sixers’ number of three-point attempts led to the Mavs going to a zone.

“We don’t shoot enough obviously, and because I was on the floor,” Embiid said. “The times I wasn’t on the floor, they were playing man. But as soon as I got on the floor, you know, they went back to that zone.

“You can’t be gun-shy. You have to fire it away, make a few and cause them to make some adjustments and probably get out of it. But we did struggle tonight against it.”

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Tobias Harris’ game was negatively impacted the most by the Sixers’ lack of activity in the second half.

The Sixers standout power forward scored 11 points on 5-for-6 shooting in the first half. However, he only had attempted two shots, making one, while scoring two points after intermission.

Sixers coach Doc Rivers thinks the inability to get defensive stops contributed to what happened.

“The zone is so much easier when they score every time,” he said. “So I thought the third quarter [when the Mavs had a 32-15 scoring advantage] set the tone. Zone is like a rhythm thing. I don’t think we got into the paint at all. We didn’t drive the [lane it] seems at all.

“I thought we had that one stretch when the second unit did it and they scored. But other that, it became one of those mental games. You drive, you miss, you stop driving. We just moved the ball on the circle.”

But perhaps trying to be positive, Rivers said the Sixers have been good against the zone most of the season.

“We’ve had a couple of [games] where we struggled,” he said. “But overall, we’ve been really good against the zone and [Friday] we were not.”

We’ll see what happens if the same situation occurs against the Bulls (33-19) on Sunday.