Joe Johnson knew what the Hawks were up against.

“For us, they've been a thorn in our butt,” he said before the game against the Celtics. “We know how tough it is to win in this building, but if we want to be one of those elite teams, we have to win in this building.”

On Friday night, the Hawks turned the tables. They pestered the Celtics under the basket with their length, beat them down the court with their athleticism, and dominated the fourth quarter to defeat them 97-86 in Boston. (Recap.)

Here are three lessons from the Celtics’ second loss of the year:

THE HAWKS HAVE GROWN UP

These weren't the 2008 Hawks. That team may have taken the Celtics to brink of elimination in the first round of the playoffs, but this squad looked better in just one game. Two years after that heated postseason series, the Hawks played their style of basketball and did not let the Celtics dictate the game.

“We just played to our strengths,” said Josh Smith. “They're a good team defensively and we wanted to keep moving on the offensive end and rotate the ball, not let it stick on one side. We played very unselfish tonight and we played great defense tonight.”

The Hawks used their length and quickness to get out in transition and prevent the Celtics from setting up on defense. The fast tempo of their game kept the C’s flustered at points.

While the Celtics are led by their veteran experience, it was the Hawks' youth that helped them win.

“We're young. We're young. But at the same time, we have matured,” said Marvin Williams. “As far as from a physical standpoint, those guys have been in the league 10, 11, 12 years and this is our fourth, fifth, sixth years. Guys are young and we play like it.”

Doc Rivers praised Hawks coach Mike Woodson for getting such a young team to play with such maturity.

“He’s a hell of a coach,” said Rivers. “I think he’s proven that. It’s amazing, when he didn’t have it, he was under heat, just like I was here. Then he gets some players and he proves he can work with players. He’s done a fantastic job there. In some ways, interchangeable parts can sometimes make it tougher. Joe Johnson can play the one, two and three. Josh Smith is a four and a three. [Al] Horford is a four and a five. So they’ve had a lot of type players, and sometimes when they’re young, it’s tough to get them to come together. I think what he’s done as well as anyone is he’s gotten them to buy in.”

Prior to the game Johnson said the Hawks had failed to put together 48 minutes of good basketball against a team of the Celtics caliber. Now they can take pride in their accomplishment.

“It feels good,” said Johnson. “We've been here numerous times and we've come up empty many times. For us to come in here and get this win early in the season, it goes to show that we've grown as a team and as a unit. We just want to build on this.”

IT TOOK A TEAM FAILURE TO GET KILLED ON THE BOARDS

“Our defense? I think we scrambled for the most part,” said Paul Pierce. “I just thought we really got hurt on offensive rebounds. I thought we did a good job initially on the first shots but like Kevin [Garnett] said, it's the second shots that really killed us.”

The Celtics were outscored 22 to 4 on second chance points. That stemmed from the Hawks' 16-6 advantage on the offensive glass. Horford contributed 13 rebounds while Zaza Pachulia and Joe Smith combined for 10 off the bench.

“Me? I just went out there and played,” said Horford. “I think if you look at it, Joe Smith and Zaza really did a great job at keeping balls alive and getting rebounds. They were really the biggest difference. Early in the fourth quarter they really set the tone for the rest of the quarter.”

Rivers says the big men were not the only ones accountable for rebounding and stopping the Hawks at the basket. He looked at the entire team for its defensive lapse.

“Unfortunately I think everyone will [say] it was our bigs, our bigs,” he said. “But our bigs weren't helped all night because the guards were getting beat off the dribble all night. And so a lot of times those offensive rebounds were guards that should have put bodies on guys. So I think the easy target is the bigs, and it wasn't them the whole game.”

Everyone on the Hawks focused on being aggressive on the defensive end to maximize their up-tempo game. The faster they grabbed the ball, the quicker they could get back down the court.

“It was very important because they're the best half-court defensive team in the league,” said Smith. “We understood if we had a lot of possessions where we were walking the ball up the court, we were playing to their style and we didn't want to get caught up doing that.”

‘THREES DON’T HAPPEN’

The Celtics entered Friday's game ranked fifth in the league in three-point shooting. They hardly lived up to the standings against the Hawks.

Rasheed Wallace was the only Celtic to connect from behind the arc as they shot 1-for-15. Over the last four games they have shot 21 percent from long range.

“I don't know whether we had good looks,” said Ray Allen (0-2 3PG). “I know I had one, I had two looks. One was in and right back out. It's hard to say. It's hard to say because we have a lot of great three shooters on the team so I think it's just a rhythm thing.”

The shots will come, Allen said after the game, but they don't happen on their own. The prolific three-point shooter is being patient this season, shooting 32.5 percent through the first 10 games. He is confident that both he and his teammates will find their shots again.

“I just think again early we just have to create an offensive rhythm and then we've got to carry that on,” he said. “Threes don't happen. Everybody's guarding the three-point line, especially if they know we're good at it. We're kicking people out of the gym by running and getting threes and running, getting lay-ups. They're going to take that away from you so you've got to get all the other things and be patient the three-ball is going to come.”