MILWAUKEE -- The Boston Celtics have known for the better part of three months that if they were to make it to the NBA Finals, they would have to go through the Milwaukee Bucks. More specifically, they would have to try to slow down Giannis Antetokounmpo, a leading candidate for Most Valuable Player of the NBA.

Whether they had three months, three weeks or three days, the Celtics knew that when these teams met in the postseason, how they fared would depend on how Al Horford played. On Sunday, he showed the world why.

In a spectacular individual performance that epitomized the best 48 minutes of basketball this Celtics team has played all season, Horford finished with 20 points, 11 rebounds, three assists, one steal, three blocks and no turnovers as Boston cruised to an emphatic 112-90 victory over Milwaukee in Game 1 of their Eastern Conference semifinal series at Fiserv Forum.

"We've said all year you can't overstate Al Horford's importance to our team," Celtics coach Brad Stevens said. "The numbers back that up."

The numbers certainly backed it up on Sunday. As the Celtics had their way with the Bucks at both ends of the floor, bringing to the fore every doubt that has hung over Milwaukee's charmed run to the NBA's best record this season, Horford found himself in the middle of all of it. Some of that came offensively, as his shooting spaced the floor and created room for Boston's guards and wings to wreak havoc in the paint, and where he and Kyrie Irving (26 points and 11 assists) had tremendous success running pick-and-pops against Milwaukee's defense.

More of it came defensively, as he led the charge against Antetokounmpo. The Bucks' star finished with 22 points and eight rebounds but shot just 7-for-21 from the field (including 4-for-16 the first three quarters of the game) and had things made difficult by the Celtics as a group -- and Horford in particular -- with every step he took.

Against Horford, Antetokounmpo shot 1-for- 6 on the day, according to ESPN's Stats & Information. Against Aron Baynes, whom the Celtics moved to the bench to try to ensure that he or Horford was out there virtually every second that Antetokounmpo was during the game, Antetokounmpo went 1-for-4.

"They were loading [the paint] a lot," Antetokounmpo said. "Lots of guys in the paint. Whenever I got in the paint, when I spin or try and change direction, the second guy was right there.

"I've just gotta go watch tape. If they are going to play like this the whole series, I have to be able to make the right pass, trust my teammates to knock down shots."

Boston entered the game with a clear game plan, which Antetokounmpo alluded to, whether Horford was on the court to guard him or not: Pack the paint, and force him to settle for jumpers. Antetokounmpo responded by going 3-for-5 from 3-point range, tying his season high for makes in a game.

But even if he makes three more in each of the remaining games of this series, if Antetokounmpo shoots 25 percent on 2-point shots -- after he hit 64 percent of them during the regular season -- the Celtics will take that tradeoff. They might not have as much success -- and they are unlikely to have more highlight blocks like the one Horford had in the third quarter -- but it's a formula that should prove successful for the Celtics if they can keep implementing it.

"I just think that our group, we all understood how we needed to defend and how dangerous he is once he gets it in the paint," Horford said. "So constantly tonight, we had a couple of breakdowns, but for the most part, I feel like everyone was very aware. Our guards really did a good job of helping and closing down lanes and things like that, and we just wanted to challenge and contest every shot as best we could."

It was a team effort that began and ended with Horford. Boston has spent the season carefully managing Horford's minutes and games played, trying to keep him as fresh as possible for the playoffs. At times earlier this season, when Horford was dealing with tendinitis, some scouts wondered if he'd be able to return to the form he showed during last year's playoffs.

But those days have been long forgotten, as Horford has been consistently excellent for Boston the past few months leading into the playoffs and remained so in Boston's sweep of the Indiana Pacers in the first round. It certainly didn't change in Game 1 of this series, either, as Horford delivered precisely the performance the Celtics needed to seize home court in this series and show why they still have a chance to do what so many expected them to do when this season began.

"He was the Al Horford we all know and love," Celtics forward Gordon Hayward said. "Knocking down shots, being able to space the floor, also taking advantage of smaller guys in the post and around the rim. Defensively, he was all over the place. [He] really did a good job on Giannis. I thought our team for the most part did a good job on him.

"It's one game, though. They're going to come back even stronger with more energy next game. So it's a good start."