Avery Bradley knows that in the second half he and his teammates hung their heads and admitted defeat. Bradley tells reporters after the Game 2 loss that they can't keep that up in the rest of the series. (0:22)

BOSTON -- As the Celtics unraveled in the fourth quarter of Tuesday's Game 2 loss to the Chicago Bulls, Avery Bradley could hear former teammate Rajon Rondo suggesting that Boston had packed it in.

And Bradley couldn't really disagree with him.

"I looked around and a few times in the game guys were putting their heads down, I think getting down on themselves," Bradley said. "But as a team, we have to stay together. The other team is looking at that. They're using that as motivation for themselves.

"I could even hear Rondo, like, 'Yeah, they gave up. They gave up.' But you never can let a team see that. You have to continue to be positive and go out there and play hard, no matter what the outcome is."

Two years ago when the Celtics were swept out of the first round of the playoffs by the Cleveland Cavaliers, fans inside TD Garden serenaded a spunky bunch of overachievers with an organic "Let's Go, Celtics!" chant.

This season, the top-seeded Celtics, having turned in an impossibly uninspired effort while absorbing a 111-97 loss on Tuesday, were booed as they walked off the court at TD Garden. Yes, expectations have understandably increased for a Boston team that won 53 games this season. But it's the way that Boston has been dominated in this series that has drawn the ire of its fan base.

After giving up 20 offensive rebounds in Game 1, the Celtics spent the 48 hours leading up to Game 2 talking about a need to be better on the glass. On Tuesday night, they gave up 10 offensive rebounds in the first half and fell behind early by double figures.

They were better on the glass in the second half, but only because the Bulls rarely missed a shot. Rondo dusted off a vintage "Playoff Rondo" performance (11 points, 14 assists, nine rebounds), and typical role players Nikola Mirotic, Robin Lopez and Paul Zipser each took turns looking like superstars against an indifferent Boston defense.

The Celtics spent much of a frustration-filled second half bickering with the officials and each other. Much of that energy would have been better spent on the defensive end; instead, they allowed the Bulls to shoot 56.8 in the second half. And Boston could never make a sustained charge.

Boston now finds itself in rare company as just the second top-seeded team under the NBA's current playoff format to drop the first two games against an 8-seed.

Here's some positivity that Bradley can lean on: The only other such instance was the 1993 Phoenix Suns, who rallied from two games down to beat the Los Angeles Lakers in a best-of-five series and went on to reach the NBA Finals.

For now, the Celtics would settle for finding a way to simply win a game.

"It's not an ideal situation for us," said Boston forward Jae Crowder. "You don't put yourself down 0-2 at home. But it's not the end of the world for us. We have the unit to go to Chicago and take Game 3. It's not ideal, but we feel like we can bounce back."

Guard Avery Bradley admitted the Celtics haven't handled losing to the Bulls as well as they should have. Brian Babineau/NBAE/Getty Images

Al Horford echoed the sentiment

"Jae said it best," Horford said. "That's all we have. Game 3 is a must-win for us."

One week ago, the Celtics were making a spirited late-season surge to capture the top spot in the Eastern Conference, aided by the Cavaliers' decision to prioritize rest over seeding. Boston entered the postseason with momentum and motivation, with some wondering if the Celtics were one of the worst No. 1 seeds in recent memory.

The team is obviously dealing with an emotional situation as All-Star point guard Isaiah Thomas tries to play following the death of his younger sister in a car accident on Saturday. Before Tuesday's Game 2, Celtics coach Brad Stevens admitted it has been quiet around the Celtics lately, in part because of Thomas' ordeal.

But the reasons for Boston's uninspired play run deeper than Thomas' emotions and this team's quest to console him.

Stevens, who is now a mere 2-10 in postseason play, must find a way to get his team re-focused.

"We have to get ready to play great on Friday," Stevens said. "That's what our focus has to be. We don't have any other choice. And that's what we said in the locker room, and that's it.

"We'll dissect the film, we'll go through it, we'll figure out what we didn't do well -- and there'll be quite a lot -- and go from there. But the Zipser, Mirotic, [Bobby] Portis, those guys have had huge impacts on the first two games of this series. I mean, I expect it from [Dwyane] Wade, right? I mean, I think we all do. Last year, I think he hit less than 10 [3-pointers] during the regular season and then more than that in the first round of the playoffs. Like, this is who he is. And it's who Rondo's been throughout his career. I mean, the level that he's playing at is terrific. And then [Jimmy] Butler [is] Butler. But those other guys are really impacting the series in a big way."

Thomas scored a game-high 33 points on Sunday, but he struggled Tuesday while putting up 20 points on 6-of-15 shooting. Stevens tried throwing a little bit of everything at the Bulls -- rolling out Terry Rozier and Tyler Zeller -- but nothing worked for very long. Boston seemed frustrated, particularly as Chicago consistently put points on the scoreboard.

Bradley refused to use Thomas' situation as an excuse for the past two games and said the Celtics need to fight through this adversity.

"You can't make any excuses," said Bradley. "Obviously, it's heavy on everyone's heart what happened to Isaiah and his family, and we were there for Isaiah. But we can't continue to say that's the reason. We just want to be there for him, continue to be there, and play hard.

"At the end of the day, we should want to play hard for each other and for him. Like, we can't sit there and keep saying, 'Oh, we're down because too much is going on.' We have to play hard, no matter what. You go through a lot throughout a season. You're going to face a lot of adversity. And the best teams overcome any type of adversity. And that's what type of team we need to be."