ATLANTA — There are nights when Josh Smith looks bored, makes silly plays, frustrates his coach and baffles his teammates.

But, oh, when he’s into the game, look out.

Smith had one of those performances in the opener of Atlanta’s playoff series against Miami, scoring 23 points and rocking the house with five spectacular dunks.

He jammed one with his back to the rim. He threw down another after grabbing a pass that seemed hopelessly out of reach.

"He’s a freakish athlete," said Miami’s Dwyane Wade, the NBA’s leading scorer during the regular season but a mere onlooker as Smith led the Hawks to a 90-64 blowout in the opener to the best-of-seven series. "There’s no one on the court, really no one in the NBA, who can match his athleticism. That’s tough. You can’t practice it. You can’t scout it."

Smith has endured his ups and downs since getting drafted by his hometown team straight out of high school. His rookie year was a real bummer — Atlanta went 13-69 for the worst record in franchise history — but he’s been part of a steadily improving team that made the playoffs in 2008 and finished fourth in the Eastern Conference this season.

It all came together Sunday night.

Smith got the Hawks rolling with 13 second-quarter points, including his own personal slam dunk contest (which he won for real as a rookie).

Joe Johnson threw an alley-oop pass to Smith, who jammed it through with ease. Then Mike Bibby upped the degree of difficulty, lobbing one up as Smith was angling into the lane. With his back to the rim, he had the presence of mind of catch the pass and pull off a reverse dunk while looking toward the other end of the court. Finally, after Wade missed a 3-pointer, Flip Murray led a fast break the other way, spotted Smith swooping toward the lane and delivered a perfect pass that he converted into a thunderous left-handed slam.

The Hawks led 59-39 at the half and were never seriously challenged.

But Smith wasn’t done. In the second half, he pulled off two more dunks, one off another lob by Bibby that seemed intentionally high, as if he wanted to see just how high his teammate could leap. Smith reached behind his left ear, snared the ball with his huge left hand and rattled the rim with such force it’s a wonder the whole thing didn’t come crashing down.

"There’s definitely an adrenaline rush that goes through your body when you do something special, like catching a tough pass," Smith said Monday, giving a backhanded compliment to his point guard. "I think Bibby really wanted everybody to see my athleticism."

That part of his game has never been in question. Smith is certainly among the NBA’s top 10 when it comes to his physical attributes: the speed and quickness that seems misplaced on someone who’s 6-foot-9 and 240 pounds, combined with a leaping ability that no one can match and the innate sense to control his body while in the air.

Miami coach Erik Spoelstra and the Heat found a grim reminder of Smith’s aerial assaults in the opener and perhaps got a bit of motivation heading into Game 2.

After Spoelstra put his team through a long film session, the Heat finally made it out for practice, about an hour behind schedule. When they looked up, the scoreboard above the court still showed Sunday night’s debacle: Hawks 90, Heat 64.

Another Smith dunk-a-thon could translate into another beat down.

"He can be a dynamic player," Spoelstra said. "When he gets out in the open court like that, he changes the game for them. He really can. A lot of those plays are above the rim. Not a lot of guys can beat him up there."

Down at ground level, it can be a different story. Smith had another solid season, but his numbers (15.6 points, 7.2 rebounds per game) actually were down just a bit from the two previous years. He’s also had an up-and-down relationship with coach Mike Woodson, including a heated exchange between the two at halftime of a game in Charlotte. The two could be heard yelling in a hallway outside the room, and Smith spent the entire second half on the bench.

Both sides insist everything is fine now, but there are still parts of Smith’s game that need improvement.

"One thing that really would define him is being a better jump shooter," Miami’s Jermaine O’Neal said. "If he keeps working, he can be one of the top 10 guys in our league. He has that much athleticism. The only thing is his jumper. He’s very, very streaky and very, very inconsistent with his jump shot."

Streaky, indeed. Smith was nearly as likely this season to score 20 points (he did that 17 times) as he was to be held to 10 or less (that happened 15 times, though he left one game with an injury and barely played in the final two games of the regular season, resting up for the playoffs). There are times he seems unstoppable, such as a 13-of-15 performance at Philadelphia late last month, and other times when he’s just plain awful.

The Heat can only hope the other version shows up when the Hawks host Game 2 on Wednesday night.

"I’m a long way from reaching the end of my full growth process," Smith said. "The sky’s the limit for me as long as I keep working hard."

He still has time to mature. Only 23, Smith would have been a rookie this season if he had played a full stint of college ball. As O’Neal pointed out, it often takes big men a little longer to develop than guards.

Smith believes all those highlight dunks have overshadowed the improvement in the rest of his game. For instance, he shot a career-best 49.2 percent from the field this season. His turnovers dipped to 2.3 a game, down from the last two years. He blocked the fewest shots of his career, but his fouls also dropped significantly.

In Game 1, he had 10 rebounds, three steals and two assists, but everyone focused on the dunks.

"We really don’t have a lot of televised games," Smith said. "People don’t get to see what I bring to the table for 82 games. When I don’t get it going offensively, I’m in there grabbing rebounds, getting assists, playing good at the defensive end."

Just how far Smith takes his game is all to him.

"His athletic ability is right there or above everybody else," Wade said. "After that, you have to put the work in to become a great player."