The Philadelphia 76ers might have the brightest young things and the flashiest new toys. But the Boston Celtics still have Al Horford. And on Tuesday, the Celtics made it crystal clear that he’s still the most confounding matchup problem facing Sixers head coach Brett Brown and his team.

General manager Elton Brand has traded away 60 percent of Philadelphia’s opening-night starting lineup and three rotation pieces. In return, he’s gotten a pair of All-Star-caliber forwards, Jimmy Butler and Tobias Harris, to run with Joel Embiid, Ben Simmons, and J.J. Redick in one of the biggest and best five-man units in the league, and an almost entirely revamped reserve corps. And yet, Tuesday’s game—the Sixers’ third loss in three tries against Boston this season, and their 10th in 12 regular- and postseason meetings dating back to 2017-18—left me wondering whether any of what Philly has changed will actually matter if the team can’t solve the conundrums that Horford causes.

On Tuesday, just as the Celtics did during their win over the 76ers in the 2018 Eastern Conference semifinals, they played without Kyrie Irving. And in Irving’s absence, Horford was once again the most important player on the floor, scoring 23 points on 9-for-16 shooting to go with eight rebounds, five assists, four steals, and just one turnover in 35 minutes of work to lead Boston to a 112-109 win at Wells Fargo Center:

Nine months after Boston drummed Philly out of Round 2, and about four months since an opening-night win that followed a similar script, the dynamic between these two teams continues to seem awfully familiar. The Sixers offense, which ran roughshod over the Nuggets and Lakers in the first two games after adding Harris, seemed stuck in the mud from the opening tip. Redick swerved around his customary diet of off-ball screens but struggled to shake Marcus Smart and Jaylen Brown; on the other end, the Celtics hunted him on the block and in the paint early, often, and successfully. Boston generated more, and largely cleaner, 3-point looks and converted them at a higher clip.

At the heart of it all was Horford, a stretch-5 who also happens to be Boston’s best playmaker and individual interior defender. Embiid insisted after the game that his counterpart had nothing to do with his own struggles: “He’s not doing anything. I was sleep-walking for three quarters, and that’s on me. … It had nothing to do with anybody.” But that’s not true. The 32-year-old remains Philadelphia’s unassuming nemesis—the quietest, most genial bogeyman in the sport.

The Celtics can gum up the Sixers offense by guarding Embiid one-on-one, making him work for position deep into the shot clock while staying glued to Philly shooters, and either harass him into a tough look or bring a late double-team that can scuttle a possession. They can drain the venom from Philly’s transition game by putting bodies in front of Simmons whenever he gets the idea to push it on the break. They can punish Embiid for playing his standard drop coverage in the pick-and-roll by bombing away from long distance off screens or drag him out to the perimeter and take advantage of his absence at the rim with timely cuts and sharp high-low feeds.

Boston can do all that because, and only because, Horford can do all of that. Despite all the “Average Al” slings and arrows he takes for producing quiet stat lines, Horford is the skeleton key that unlocks the Celtics’ best self, and that locks the Sixers up along the way. And even when Philly was able to battle through, riding Butler’s shot creation on isolation plays (22 points on 7-for-12 shooting, nine rebounds) and a late surge from Embiid (15 of his 23 points came in the fourth quarter) to get within arm’s reach of the win, it was Horford who helped slam the door.

First, he came up with a one-on-one stop against Embiid with 33 seconds left—a play Embiid wanted a foul call on and appeared to have an argument for (one he made somewhat indelicately after the game). That led to a huge dunk by Smart, which put Boston up four with 23.9 seconds to go. Then, after a Butler layup and the foul cut the deficit to one with 16.1 ticks left, Horford took an inbounds pass, got fouled, stepped to the line for the first time all night, and calmly sank what wound up being the game-winning free throws—a fittingly quiet cap on yet another frustrating night for Philly against the guys in green.

Last season’s series echoed up and down the stat sheet. The Celtics shot 13-for-29 from 3-point range Tuesday; they averaged 12 long-distance makes and 32.2 attempts in the 2017-18 series. The Sixers shot 9-for-27 on Tuesday from 3; they averaged 8-for-27 last May.

Embiid spent most of the first three quarters bottled up, and he finished with 23 points on 9-for-22 shooting (40.9 percent), a 2-for-8 mark from 3-point land (25 percent), 14 rebounds, and three assists. His averages in the conference semis: 23 points, 14 rebounds, and 3.6 assists per game, shooting 44.1 percent from the floor and 23.8 percent from deep. Redick finished with 16 points on 4-for-11 (36.4 percent) shooting; he averaged 16.4 points on a 43.5 percent mark against Boston in the playoffs.

Even signs of progress came attached to reminders of how far Philadelphia has to go. Simmons largely looked more decisive Tuesday than he did in last season’s playoff matchup, attacking for 16 points on 7-for-9 shooting to go with five rebounds, five assists, and a pair of steals. But the Celtics still slowed him down in transition—after racking up 41 fast-break points through two games since the Harris trade, Philly managed just 12 on Tuesday—and his wonky shooting reared its head again, with five missed free throws looming large in a three-point defeat. (Ditto for Butler, who chiseled his way to 10 freebies but missed three big ones in the fourth quarter.) Just as McConnell did last spring, he provided a spark in the backcourt, scoring nine points with three assists and playing aggressive defense in 13 minutes off the bench … but all that did was underscore the fact that the Sixers continue to need him to punch above his weight class in a matchup like this, because the soaring talent who was supposed to occupy that spot never made it off the launchpad.

And as great as Harris looked against the Nuggets and Lakers, he wasn’t equal to the challenge against Boston. The new arrival missed 10 of his 14 shots, including all six of his 3-point attempts, a number of which were precisely the sort of momentum-swinging, wide-open looks Philly needs him to knock down when defenses force the ball out of Embiid’s hands. On the other end, Marcus Morris took the fight right to Harris from the early going, muscling him up in the post, getting to his preferred spots, and firing confidently on his way to 17 points on 7-for-13 shooting; three nights after calling his team onto the carpet, Morris confirmed after the game that this, in fact, was fun.

Something else that likely sparked joy for a number of Celtics fans: Gordon Hayward serving as the second-unit game changer that Philly couldn’t match.

Hayward was fantastic Tuesday, scoring a game-high 26 points on 8-for-11 shooting, including a 6-for-7 mark from 3. He targeted reserves Furkan Korkmaz and Boban Marjanovic in the pick-and-roll, and every time they gave him some space, he made them pay. Tuesday’s big game continued the long-awaited uptick for the former All-Star, who’s shooting 49.5 percent from the field and 38.5 percent from behind the arc since January 1. Even with Irving sidelined, Hayward’s pick-and-roll playmaking and pull-up-shooting game give the Celtics a wrinkle they didn’t have in last season’s series. The Sixers hoped they’d get their infusion of that sort of play from Markelle Fultz, but the version of him they needed against Boston never showed up.

There are still buttons that Brown can push in his search for solutions against Boston. The minutes in which Hayward carved up Korkmaz seem to be the exact minutes that James Ennis—a longer, stronger wing, and a significantly superior defender—should be playing. The more mobile Jonah Bolden might also make a better match for center minutes than the lumbering Marjanovic. And if one or two Harris jumpers had rolled in rather than out, one or two Simmons or Butler free throws had gone down, or Embiid had got that bang-bang call on Horford in the final minute, we might be having a different discussion. And oddly, we might be if Irving had played, too; while he was brilliant in Boston’s Christmas Day win, he’s also just the sort of iffy defender that Philly could hunt and peck with its new supersize lineup, just as the Celtics did to Redick and McConnell.

These two teams are both really good; the margins here aren’t massive, but the more I see this matchup, the more I get the sense that Boston has locked down an advantage. The Sixers, and Embiid in particular, have the talent to change the conversation. At some point, though, they’re going to have to come up with some new answers to the same old problems.