Even if Al Horford had three layers of rust upon his return to the NBA after missing 58 straight games with a torn pectoral muscle, he was going to help the Atlanta Hawks. When a 25-year old All-Star — in no matter what shape he might be — replaces Erick Dampier, Jason Collins and/or Ivan Johnson, he’s bound to help matters, even if his greatest presence comes as a decoy to draw some of the Boston Celtics’ attention.

But Horford showed in Game 5 he’s no decoy. He jumped right back into being a low-usage menace, one who hits open jump shots, draws dunks out of dives to the hoop and plays with an activity and motor most young big men should attempt to replicate.

John Hollinger of ESPN noted that Horford has an opportunity to turn the Hawks into a serious problem for the Celtics. (ESPN Insider)

Horford gives them just enough offensive competence to pose a threat to Boston. The Hawks have struggled all year, and really all throughout the Joe Johnson era, against elite defenses. Boston in particular gives Johnson fits. After he destroyed them single-handedly in Game 4 of the first round in 2008, the Celtics basically decided that somebody else would do the damage from now on, and have loaded up on Johnson ever since.

Johnson’s slow decisions with the ball and the coaching staff’s willingness to iso-Joe themselves into oblivion have helped prevent Atlanta from having much success against the Celtics offensively, but Horford’s return (and Josh Smith’s return, after he missed the end of Game 2 and all of Game 3) provides hope they can score more consistently.

And they don’t need to score a ton. Here’s the dirty little secret about the Celtics that most everybody overlooks: They stink at offense. Boston was 24th in Offensive Efficiency in the regular season at 98.9 points per 100 possessions, putting it right between New Jersey and Toronto. Every other playoff team was above the century mark. In the playoffs, against a team with no center (and no bigs whatsoever in one of the five games), the Celtics have been worse: just 94.7 points per 100 possessions.

Thus far they’ve survived by strangling the Hawks’ offense; Boston leads all playoff teams in Defensive Efficiency. But if Horford can make the Atlanta offense merely below-average rather than awful, the Hawks can do this.

Not that they’re likely to, mind you: AccuScore gives Atlanta just a 17 percent chance, partly because their model favors Boston’s experience. But the Hawks are no strangers to the playoffs anymore, and the franchise’s almost supernatural ability to make the second round of the playoffs before flaming out (15 times in 41 years) gives it an odd slice of history in its favor.

Despite everything that went wrong for the Celtics in Game 5 — Rajon Rondo took three quarters to wake up, Paul Pierce hobbled around like he was old enough to be Dampier’s father, Kevin Garnett didn’t get enough touches, Horford returned to All-Star form and the Celtics’ defense seemed to have several more breakdowns than usual — they had the ball on the final possession with a chance to win the game.

But it’s too simple to say, “Because all of that went wrong and the Celtics still lost by just one on the road, they’re destined to win by 20 at home in Game 6.” Every NBA playoff game is a different creature entirely. It’s like if I went to a pitcher’s mound and tried to throw a fastball down the middle seven consecutive times. The first one right go right down the pike, the second might miss the outside corner by three inches and the third just might hit the batter in the head. There’s a degree of error in my throws, just like there’s one in the NBA playoffs, and a lot can change from one night to the next. Think about the difference in Horford from Game 4 to Game 5: He felt rusty and out of shape in his first game back, then came close to dominating in his second.

What am I trying to say here? Horford could become the difference in this series. He could lead the Hawks to three straight wins and become a hero in Atlanta for returning ahead of schedule and leading an upset. Or, he could have an average game tonight, get outplayed by Kevin Garnett and be fishing off the coast of Florida this time tomorrow.

The Celtics need to do a better job limiting Horford’s easy looks. Most of his hoops in Game 5 were dunks and wide open jumpers. If they can do that, he might go back to looking like a rusty center who missed 58 straight games rather than the tour de force he became in Game 5.

His presence, though, certainly opened things for the Hawks and made their offense seem considerably more natural.