MIAMI — The Nets’ season is 47 games old and they have only nine wins, but coach Kenny Atkinson generally has remained as upbeat as the old children’s TV host Mister Rogers. That changed after two straight losses in which the Nets allowed the Cavaliers and Timberwolves to average 126.5 points and shoot .522 from the field.

Atkinson said the only way to overcome opponents with superior talent is to compete harder and play physical defense. He told the media that lineup changes are a possibility, and he delivered the same message to his team Saturday night before heading to Miami to take on the red-hot Heat on Monday night at American Airlines Arena. The Heat (18-30) has won seven in a row.

“We’ve got to find the guys that want to defend and distribute the minutes proportionally, appropriately,” Atkinson said. “I think we’ve had a streak where we’re not defending. That’s not acceptable. That’s not the type of program we’re trying to run.”

Reacting to Atkinson’s threat to his players after a 129-109 loss at Minnesota, center Brook Lopez said: “It’s obviously something we have to deal with as players. I don’t know if lineup changes would do that, but we need guys out there from the jump who are going to be ready to play and ready to compete.”

The Nets’ 2-21 road record easily is the worst in the NBA, and they have lost 16 of their past 17 games overall. The 109 points they gave up to Miami in a three-point loss Wednesday night at Barclays Center is their best defensive performance in the past nine games.

Sean Kilpatrick said the Nets have allowed opponents to get “too comfortable,” as they did Saturday night, when the Nets trailed by 15 midway through the opening period.

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“They came in hitting almost every shot,” Kilpatrick said. “It goes back to the physicality thing. If we jumped on them and were a little bit more physical in the first quarter, then they don’t grab a rhythm the way they did.”

Part of the problem against the Timberwolves was that power forward Trevor Booker, who is considered the Nets’ best defensive player, quickly picked up three fouls and played just over six first-half minutes.

“I try to be physical, and it didn’t work out in my favor,” Booker said. “Hopefully, the next game it will. They hit a couple shots and they got pretty confident and it was tough to slow them down from there.”

Notes & quotes: According to an NBA source, the Nets have signed forward Quincy Acy for the rest of this season and will make a formal announcement Monday. “He gives us a physicality I think you need in this league,” Atkinson said Saturday.