The Boston Celtics will no doubt beat the defending champion Milwaukee Bucks in the second round of the playoffs if Jayson Tatum is the series' best player.

That may seem like a tall order considering Giannis Antetokounmpo continues staking a forceful claim as the best player in the world, but so did expecting Tatum to outplay Kevin Durant in Boston's highly anticipated first-round matchup with the Brooklyn Nets. Four games later, Durant had labored through arguably the most disappointing playoff effort of his career, unable to free himself the shackles of Tatum and Boston's historically elite defense.

Antetokounmpo presents a more imminent and inevitable challenge than Durant, though. Tatum will surely spend some time checking the reigning Finals MVP, more a result of the Celtics' switch-heavy scheme than his ability to limit Antetokounmpo one-on-one. No truly elite player can be guarded in isolation, especially during the playoffs. Boston will present multiple lines of defense on the backside to keep Antetokounpo out of the paint, daring him to shoot jumpers.

Point-of-attack defense still matters, though, one of the many reasons why Al Horford's performance could be a Celtics bellwether against the Bucks.

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Celtics' X-Factor vs. Bucks: Al Horford

The 35-year-old has enjoyed as much success defending Antetokounmpo as any other player in basketball during the latter's increasingly epic career. But Horford's best stints against him came a few years ago, before the former entered the twilight of his prime and Antetokounmpo won the first of his two MVPs and hoisted the Larry O'Brien Trophy last June.

It's foolish to think Horford, even after turning back the clock in the first round against Brooklyn, will be able to keep Antetokounmpo in check by himself. Ime Udoka won't task him or any other Celtics defender with that impossible assignment full-time. But Horford is poised to get the lion's share of minutes guarding Antetokounmpo, just like he did the one time both players were healthy when Boston and Milwaukee faced off during the regular season.

No other player on the Celtics' roster, with the possible exception of designated rim-protector Robert Williams III, boasts a better combination of length, strength and quickness than Horford. If he can keep Antetokounmpo from creasing the paint, aided by active and aggressive help behind him, it'll go a long way toward Boston dethroning the champs.

The Celtics can live with Antetokounmpo hitting mid-rangers over Horford. What no team can survive is Antetokounmpo consistently getting loose in the open floor, attacking his primary defender without a wall built at the restricted area.

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Making life tough on Antetokounmpo is all that Horford and the Celtics need to accomplish in this series, a challenge made far easier by the absence of Khris Middleton. There isn't a defense in the NBA that provides more disruptive help than Boston. With Middleton sidelined, expect the Celtics to make Antetokounmpo see even more bodies behind the initial line of defense, no matter who's guarding him.

Horford will factor into that dynamic as a help defender when Boston switches screens involving Antetokounmpo on and off the ball. He'll also spend ample time guarding Jrue Holiday after switches, a matchup that could swing this series.

Horford showed against Kevin Durant, Kyrie Irving and the Nets that he's still an effective switch defender. Holiday isn't Brooklyn's superstars as an individual scorer and playmaker, but his improvements as a pull-up three-point shooter make him a tougher guard for Horford than he was even last season. Holiday's elite 40.6% shooting on off-dribble triples during the regular season, per NBA.com/stats, didn't extend to the first round, though, when he went 4-of-16 against the Chicago Bulls.

No matter who's guarding him, Horford included, keep an eye on Holiday's pull-up in the second round. It's difficult to imagine the Bucks advancing to the Eastern Conference Finals sans Middleton if Holiday doesn't have his jumper working.

Of course, Horford's importance against Milwaukee won't come solely on defense.

The Bucks allowed more three-pointers during the regular season than every team in basketball but the Miami Heat, per Cleaning the Glass, an intentional consequence of a defense built to protect the paint first and foremost. They won't lay off Horford at the arc to the same extent the Celtics will Antetokounmpo, but rest assured that Milwaukee will give him ample opportunity to launch from three—especially above the break.

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Horford shot a red-hot 9-of-15 on threes in the first round, including 4-of-7 from above the break. Though it seemed like he let fly with newfound frequency and confidence against the Nets, Horford actually attempted fewer triples per 100 possessions than he did during the regular season.

Anticipate that changing in the second round whether or not Horford has his shot going. Just like his potential all-court impact versus Antetokounmpo and the reigning NBA champions, Horford's proficiency from three will loom extremely large to the outcome of a second-round series that has major title implications.