Paul Pierce and the struggling Celtics will have to contend with LeBron James, right, and the Cavaliers, who will be seeking some payback tonight.

The Providence Journal / Glenn Osmundson

BOSTON — The Celtics are in the midst of their worst slump since the trades for Kevin Garnett and Ray Allen helped revitalize the franchise.

They have lost six of their last eight games, including three straight, and five of their last six on the road.

They have lost their swagger, and they must face a hungry Cleveland Cavaliers team (28-6) tonight at Quicken Loans Arena, where the Celtics (29-8) have lost nine straight.

The Cavs will not only be looking to avenge their first loss of the season, but they’ll be seeking a little payback for the Celtics eliminating them from the playoffs last season.

The odds are stacked against the Celtics tonight, but they are looking forward to the matchup.

Boston captain Paul Pierce believes the team can turn things around against Cleveland by becoming the first team to beat the Cavaliers at Quicken Loans this season.

“They are the best home team in all of basketball, so they have been looking forward to this,” Pierce said. “We’re going to get their best punch. When you play a team like this, teams like us try to find the edge because we know somewhere down the road we’re going to see them in the playoffs. We have to be ready for their best shot. The way they have been playing at home has been unbelievable, but the way we are playing, this is a great way to get back on track.”

Boston coach Doc Rivers is looking forward to seeing how his team responds to its recent adversity.

“That is not a bad test for us,” Rivers said. “It’s going to be a tough game. They are playing unbelievable basketball. … Maybe it will be something to get us going.”

The Celtics must find a way to contain Cleveland superstar LeBron James, who is averaging 27.4 points, 6.6 rebounds and 6.6 assists.

James told Cleveland reporters that he expected the Celtics to play much better than they have been.

Containing James is difficult for any team, but it may be especially so for the Celtics, who have struggled to stop teams during their recent slump, especially in the fourth quarter.

Pierce said the number-one reason the Celtics are struggling is because they have not been playing good enough defense.

“Right now, our defense is not getting the job done,” Pierce said. “When you look at us, that’s one of the first things we talk about. That’s the type of team we are, and when we don’t defend, it doesn’t allow us to get out and run the break. We’re not causing turnovers like we want to.

“Our goal is to go out there and shut things down. We are allowing too much dribble-penetration. I told the guys we need to get our defensive swagger back. It’s been broken these last 10 or 12 days.”

His teammates agree.

“Our defense is breaking down a little too much,” forward Leon Powe said. “That’s something we stress; it’s defense first and the offense will come. But it’s been breaking down. People are getting in the lane, getting offensive rebounds. We have to buckle down and make a commitment, and hopefully everything will pull through.”

Garnett said, “We have to get our swagger back, and some of the things we talk about are being defensively sound. This is the difficult part of the year. I feel we have the mindset to weather the storm.”

Rivers said the coaching staff knows what the problems are and knows how to fix them, but the Celtics have not been practicing because of their grueling schedule, so the problems aren’t being fixed.

No team had played more games than the Celtics through Wednesday, and they have had only two full practices since Dec. 23.

Rivers says the Celtics are still a confident team even though they have been struggling to regain their focus.

“They have the ultimate confidence,” Rivers said. “Our goals haven’t changed.”

Said Pierce, “We know what we’re capable of; it’s just about going back to the basics and doing what we do.”

Tonight, the Celtics hope to prove they are still the best team in the NBA.

“The confidence is still there,” Pierce said. “It’s a long season, and that’s what we try to tell each other. We bend but we don’t break. That’s what it is all about. We preach the word ubuntu, and what it means is that through the difficult times, we stay together. Nobody’s pointing the finger. It’s a tough stretch, but we know what we are capable of.”

roblee@projo.com