Inside the Al Horford-Giannis Antetokounmpo showdown: How the Celtics’ big man made a difference

When Al Horford was gone from the Celtics, playing with the rival Philadelphia 76ers, former Celtics coach Brad Stevens’s best option in defending Bucks star Giannis Antetokounmpo was former second-round pick Semi Ojeleye.

Ojeleye was a physical defender, with enough bulk, built by his legendary postgame weight room sessions, to withstand the physical contact created by Antetokounmpo’s punishing post moves.

Now that Horford has returned, the Celtics have a veteran who can provide better resistance, which, at times, can be effective against the two-time MVP. Celtics coach Ime Udoka, like all of the 28 other NBA coaches, is resigned to the fact Antetokounmpo is going to score on any defense, whether he drives through a defender, around a defender, or past a defender.

What the Bucks have tried to do in this Eastern Conference semifinal series is set screens on Horford and Grant Williams and leave Jaylen Brown to guard the 7-footer.

The Celtics gave up that switch too easily, meaning they allowed Brown to be one-on-one against Antetokounmpo and he lost that battle most of the time. What’s more, the key to the Bucks’ Game 3 win were those matchups between Antetokounmpo and Brown. Antetokounmpo hit two key buckets when defended by Brown in the last six minutes.

Bucks coach Mike Budenholzer is showing Horford the ultimate respect by setting those screens to avoid a Horford-Antetokounmpo matchup. Horford is big enough to challenge Antetokounmpo’s shot and physical enough to prevent getting bullied by his drives.

Through four games, Antetokounmpo is shooting 43.9 percent on 28.5 shots per game. He’s averaging 32 points per game because of his volume of shots, not necessarily his efficiency. Antetokounmpo was a 55.3 percent shooter during the regular season. The Celtics have also allowed him to shoot open 3-pointers — the better alternative to punishing drives — and he’s missed 14 of 16 of those shots.

Giannis Antetokounmpo and Al Horford have spent much of the first four games of the playoff series going head-to-head.Jim Davis/Globe Staff

The resistance from Horford and others, along with the constant offensive responsibility, is tiring Antetokounmpo, and the Celtics sensed fatigue in Game 4. His defense against Horford slipped. It was the 35-year-old Horford who had more energy than his 27-year-old counterpart.

“With adrenaline, you feel great,” Horford said about his physical energy. “I feel fine. Can’t wait to go home, rest up, and be back in Boston.”

Horford has been the primary reason why the Celtics are tied in this series and were a basket away from sending another game into overtime. He has emerged as the team’s third offensive option and he has helped expose a Milwaukee defense that protects the paint fiercely but allows teams to shoot open 3-pointers.

Horford has made 14 of his 28 3-point attempts, including 9 of his 14 in Milwaukee. The scouting report on the Celtics says to allow Horford and Marcus Smart to shoot, if that takes shots away from Brown and Jayson Tatum. But Horford has been such an effective offensive player, the Bucks are likely to make adjustments in Game 5.

“Horford was good, he was good the entire game,” Budenholzer said. “He made several big plays and big shots in the fourth quarter. The NBA is a lot about a two-man game and [the Celtics] are in a good place and Horford is shooting it at a high level. We’re constantly discussing and trying to throw different looks.”

It’s been a difficult journey for Horford since 2019 when he decided to sign with the Philadelphia 76ers — a four-year, $109 million package — and be a complement to Joel Embiid on a title-contending team. The 76ers quickly found out that Horford struggled with Embiid, who takes up too much space in the paint.

Horford then tried to become a stretch four — a power forward who mostly plays on the perimeter and shoots 3-pointers — and it failed miserably with Ben Simmons being a non-threat, thereby allowing defenses to shift to Horford.

Al Horford, heading for the visitors locker room before the start of Game 4, has played a sizable role in the success of the Celtics this postseason.Jim Davis/Globe Staff

Not only did Horford enjoy a successful stint with the Oklahoma City Thunder, who acquired him strictly for his salary and as a trade chip, but he was able to get some rest when the Thunder told him to stay home because they decided to invest fully into their youth movement.

When the Celtics’ season started in late October, Horford had not played since March 24. After years of dealing with knee issues and playing heavy minutes, Horford needed a break, and that time off energized his body while the trade to the Celtics energized his spirit.

Always one of the better defending big men in the NBA, Horford has continued to contain opponents even at an advanced age. It’s a byproduct of taking care of his body, digesting Udoka’s defensive techniques, and still having enough game left for nights like Game 4.

“He’s been a calming influence throughout the whole year,” Udoka said. “He’s been there and done that, been on a lot of playoff teams that have gotten really far and made really big runs. He’s a veteran of our group and he’s done it all year. We know he’s been great throughout training camp, early in the season and has carried that into the playoffs and he’s almost took another step [forward] in the playoffs.”

Gary Washburn is a Globe columnist. He can be reached at gary.washburn@globe.com. Follow him @GwashburnGlobe.