ATLANTA – The Boston Celtics lost Game 1 — and they may have lost their floor leader for Game 2.

Josh Smith scored 22 points and grabbed 18 rebounds as the Atlanta Hawks built a big lead early, then held on for an 83-74 victory over the Celtics in the opener of their Eastern Conference playoff series Sunday night.

But this one will be remembered for what happened in the final minute, not the Hawks’ blistering start. While complaining about a call, Boston star Rajon Rondo was ejected for bumping an official and faces a possible suspension.

Game 2 is Tuesday night in Atlanta.

“I didn’t intentionally chest-bump him, but that’s what it appears to be,” Rondo said.

The Hawks, who led by as many as 19 in the first half, were clinging to a four-point lead when Rondo lost his cool with 41 seconds remaining. Boston’s Brandon Bass was called for a foul on Smith tussling for a loose ball, with both players sprawled on the court. Rondo screamed at official Marc Davis, who quickly called a technical. Rondo then bumped Davis with his chest and was tossed out.

Rondo, who scored 20 points and dished out 11 assists, clearly appeared to stick out his chest to strike the official. That’s a huge no-no and will almost surely draw the wrath of NBA Commissioner David Stern.

“It’s out of my control,” Rondo said. “Obviously, I want to be there for my teammates but other than that, it’s out of my control.”

Getting in some immediate lobbying, Celtics Coach Doc Rivers saw things a bit differently than the replay showed. Not surprisingly, he doesn’t think Rondo deserves a suspension.

“I’m always worried, but I would be surprised if that happens,” Rivers said. “I thought Rondo was walking toward Marc, and Marc turned back toward him, and that’s when Rondo bumped him. … That’s all it was, in my opinion. But we’ll see.”

Rondo had a similar take.

“Obviously I was upset about the call and I said some words to Marc. I deserved the first tech,” Rondo said. “As I was walking, I thought he stopped. My momentum carried me into him. I even think I tripped on his foot.”

At the beginning, the Hawks looked much quicker and faster than the aging Celtics. With every starter outside of Jason Collins contributing at least four points, Atlanta raced to a 20-6 lead with the game just over 5 minutes old. The Hawks twice pushed the margin as high as 19 points and settled for a 49-35 edge at halftime.

Smith totally outplayed Boston’s Kevin Garnett over the first two quarters, going into the break with 15 points, 11 rebounds and two assists. Garnett had only two points on 1-of-9 shooting.

“He was an animal,” Atlanta Coach Larry Drew said of Smith. “When he’s playing with that energy, he just makes us so much better.”

Smith had to carry the load. The Hawks’ other big scorer, Joe Johnson, had a miserable night with 11 points on 3-of-15 shooting. He was 0 of 9 from 3-point range.

The Hawks got sloppy with the ball and made only 20 of 60 shots after their blistering performance in opening quarter. That allowed the Celtics to edge back into the game, and it looked as though they might pull off the comeback until Rondo’s big blunder.

“We came out like our jerseys were going to win the game, because we’re the Celtics,” Rivers said. “You’ve got to play to win the game.”

Smith said he was definitely fouled as he scrambled for the loose ball with Bass.

“That was the right call they made,” Smith said of the potentially series-altering play. “I’m not sure what happened with Rondo. That will be up to the league to see what he did wrong. You never know what’s going to happen, but we’ll definitely factor him in going to tomorrow.”

Garnett finished with 20 points and 11 rebounds. Paul Pierce had only 12 points, going 5 of 19 from the field and missing all six of his 3-point attempts.

“For us to win, I have to be a better player,” Pierce said. “I was a really big culprit.”

Celtics guard Ray Allen missed a playoff game for the first time in his career, watching from the bench in a suit and tie because of an ailing right ankle.