BOSTON — Prior to this season, Celtics star Jayson Tatum called a meeting of their "six starters," mostly to ensure everyone was cool with whoever would be left out of the starting five. Sixteen years into his NBA career, Al Horford accepted the reserve role, knowing his No. 42 would still be called when needed.

And Horford is needed, now more than ever, as Kristaps Porziņģis has been diagnosed with a right soleus strain, which cost the starting Celtics center Wednesday's first-round, close-out win over the Miami Heat.

"The way that I approach things, it's about whatever I can do to help our team win, put us in the best position, and how I can impact a team with that," Horford told Yahoo Sports. "And my mindset was simple. When that happened, I had a choice to make, and ultimately I know what I can bring to a team and the things that I can do. I just had to do it in a different way now and in a way that I'm not used to.

"Ultimately, it was like, 'I accept it, I stay the course, and when my opportunities come ... I'll be ready for that.' Throughout the season, it happened, and now that it's happened, I had to be ready to step up."

Wednesday's 118-84 win in Game 5 gives the Celtics some time to sort out Porzingis' status. It is a difficult injury to assess. Return too soon, and Porzingis could put his Achilles' tendon at risk. Recovery time lasts an average of 17 days, according to In Street Clothes, but more severe strains can extend that timeline to six weeks. That is the difference between a return in time for the conference finals and possibly missing the NBA Finals.

"We're just going to give it a week and see where he's at," second-year Celtics coach Joe Mazzulla said of Porziņģis' injury prior to their Game 5 win, "see how he responds to the treatment over the next week."

Milwaukee Bucks star Giannis Antetokounmpo suffered a soleus strain on April 9 and has not played since. Twenty-two days later, he is listed as doubtful for Thursday's Game 6 against the Indiana Pacers.

Boston's backup center, Luke Kornet, who will also see increased minutes in Porziņģis' absence, just returned from a milder soleus injury in a week's time. Porziņģis' reaction to his strain did not look mild, although he posted on X (formerly Twitter) shortly afterwards: "Thanks for all the support, will be good."

It sure sounds like we have not seen the last of Porziņģis.

"He wants to be out there bad," said Jaylen Brown, Porziņģis' carpool partner, who scored a game-high 25 points in just 26 minutes of the close-out victory. "Just knowing him now, he's smiling, but you can tell it hurts him not to be with his team. But I just told him, 'You know we're going to hold it down. Just get your recovery in, get back healthy, and we're not going to miss a beat when you come back, so we'll be ready."

Either way, Horford and Kornet went to work on Wednesday, the bigs for a championship favorite, a soon-to-be 38-year-old and an NBA journeyman. They combined for 10 points (on 4-for-5 shooting), 13 rebounds and five assists in 41 minutes of another blowout of the Heat. The Celtics hardly needed Porziņģis against undermanned Miami. Nor may they need him in a second-round set against either the Cleveland Cavaliers or Orlando Magic. Heck, they might walk through the conference finals without him.

"We still have tests to go through throughout these playoffs, especially now with KP out, but I think we're up to the challenge," said Brown. "I'm excited about that. We're graduating. We haven't graduated — yet."

Remember, Horford is no slouch. He is a five-time All-Star, even if his last appearance came six seasons ago. He started for a Celtics team that reached the Finals just two years ago. LeBron James is the only active player who has played more postseason games than Horford. So, when Miami's Bam Adebayo ran through Horford's screen on the opening play of Game 5, trying to set a tone, it hardly fazed the veteran.

"My mindset is still the same," said Horford, who registered all three of his assists in Boston's 41-point opening quarter, burying the Heat. "I want to bring energy and have an impact on the game. I just think that probably I will be put into positions to at times make more offensive plays, and I think tonight we saw it. In the first half, JT was getting doubled, and he's kicking it to me, and I'm finding guys for shots. When I come off the bench, it's usually in a different context. I'm more spacing and things like that."

"One of the things coming into the season was being able to win games in different ways with different lineups," added Mazzulla, who wants to play faster in Porziņģis' absence. "Even when KP was healthy, we still played small, did a bunch of stuff, played double bigs, so you just have to develop a bunch of different identities to be able to get into different playoff series, when you have different matchups, and we've been able to do that because of the guys' attention to detail and their buy-in towards making the most sense, doing whatever it takes to win that particular game and having different identities."

Wednesday marked Horford's 75th playoff game with Tatum and Brown. (By comparison, Joe Ingles and Gary Harris are the only members of the Magic who entered this season with more than eight playoff games under their belts.) Their chemistry smooths Boston's transition from one starting unit to the next.

"It's helped a lot," Horford told Yahoo Sports. "We've had a lot of success here, and I've played from JB's rookie year — and Jayson's rookie year as well — so there's a level of comfort and trust with one another that we have. I'm trying to make the game easy for them and trying to find ways that I can impact, and I feel like we just kind of feed off each other. The work that we've put in, it's going to show. We're not trying to figure things out together. We've been doing this for a lot of years, and I feel like you can tell."

Horford is also the spiritual guide of these Celtics. Tatum and Brown have called Horford "my favorite teammate I've ever had" and "one of the best off-court leaders in the NBA," respectively. Midway through the second quarter on Wednesday, Horford grabbed consecutive offensive rebounds, drew a foul and flexed in front of Boston's bench. The TD Garden crowd roared. The Celtics will rally around the veteran.

"Al sets the temperature for us with his ability to impact the game basketball-wise but also with his personality and his aggressiveness," said Mazzulla. "He set the tone for us, and everybody followed suit."

But Porziņģis was always the component that unlocked another level to this team. The Celtics traded Marcus Smart, the heart and soul of five Eastern Conference finals appearances, for the 7-foot-3 Latvian. Porziņģis can shoot over anyone from anywhere. His verticality is as much a deterrent on defense as it is a benefit to Boston's offense. His is a dimension the Celtics have not had, save for the second half of the 2021-22 regular season, when a healthy Robert Williams III also transformed them into world-beaters.

And health was always the question. It is the reason they traded Williams and the reason they were so careful with both Porziņģis and Horford on back-to-backs all year. Porziņģis has never been fully healthy for a playoff run in his nine seasons. He tore his right meniscus in Game 1 of the 2020 playoffs, and he carried his knee soreness into a 2021 first-round exit. He lasted until his fourth playoff game this season.

The Celtics are better with Porziņģis. There is no question about that, even if they are now 22-4 without him. The starting lineup of Porziņģis, Tatum, Brown, Jrue Holiday and Derrick White outscored opponents by 12 points per 100 meaningful possessions during the regular season, rivaling the defending champion Denver Nuggets' vaunted starters, according to Cleaning the Glass. With Horford in place of Porziņģis, that five-man unit was +1.3 points per 100 non-garbage possessions, closer to Cleveland's starting lineup.

Miami was no match for these Porziņģis-less Celtics. The real tests begins now, as the size of either the Cavaliers or Magic could create problems, and it only gets harder from there. No. 42 is ready for his call.

As Horford told Yahoo Sports, "I feel like I'm always ready to go."