Perhaps the surprise is that it took this long, but the Nets have hit their first major bump in the long road known as the NBA season. After a 4-5 start that exceeded all expectations, they have three straight losses that coach Kenny Atkinson attributed to “defensive slippage.”

In their previous five games, the Nets went 3-2 and allowed a respectable 104.8 points per game. But they were steamrollered for 125.3 points per game in road losses to the Clippers, Lakers and Thunder.

All three of those teams would qualify for the Western Conference playoffs if they began today, so the caliber of opposition definitely was a factor. But the drop-off in performance has been so steep for a relatively young team that still is learning to play together that Atkinson expressed concern.

“Playing a pretty good team in the Clippers was one issue,” Atkinson said. “On the road sometimes with a new group, there’s slippage. We’ve got to get back together. We’ve got to see if we can get some stops when we get home.”

The Nets (4-8) will try to regroup against Portland (7-7) at 3:30 Sunday afternoon at Barclays Center. The Trail Blazers arrive on a three-game losing streak of their own, and they are experiencing similar problems in that they rank 29th in opponent scoring, allowing 112.4 points per game, and 25th in rebounding.

The Nets have struggled recently against some of the league’s top point guards, and the Blazers’ Damian Lillard, who is averaging 28.7 points per game, belongs in the class. He’s paired in the backcourt with C.J. McCollum, who is averaging 22.1 points per game.

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How does a young team handle this first stretch of adversity? “It’s on us,” center Brook Lopez said. “It’s all fixable stuff, and it’s something we have to recommit and refocus on in the next few days. We’ve got to focus on a lot of the little things, a lot of the details we need to pick back up, and get back to what we were doing beforehand.”

Asked if the young players need to hear his voice of experience, Lopez said, “I don’t think I need to say much. I love the group we have. It’s not a question of heart or intensity or energy or anything like that. I think it’s just getting back to our basics, getting back in the habit of playing defense our way.”

If there has been a pattern to the Nets’ losses, it’s a tendency to dig a hole in the third quarter, which is what happened against the Thunder even with Russell Westbrook resting. “We need to be more consistent defensively,” backup center Justin Hamilton said. “We need to keep working and focus on it the whole game.”

After five straight road games, the Nets play five of their next six games at home, which might provide a lift. “When you hit a bump in the road, guys think they need to do their own thing, but it’s just trying to keep everybody together and just try to stay positive,” Rondae Hollis-Jefferson said. “It’s a long season.”