The Celtics are surrounded by the ghosts of playoffs future and past. It’s hard not to wonder how good they will be next season, when Kyrie Irving and Gordon Hayward return. It’s even harder to forget how easily they were beaten by LeBron James and the Cavs in last year’s Eastern Conference finals. We may end up remembering this season as a transition year for the franchise, but the team’s 4-1 second-round victory over the 76ers, who were one of the hottest teams in the NBA, is proof these players are a special group in their own right. Brad Stevens is great, but he’s not coaching a bunch of scrubs. They have the players to at least put a scare in LeBron.

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They don’t have much in common with last year’s team. Al Horford and Marcus Smart are still the defensive backbones of the team, but Jaylen Brown and Terry Rozier have taken quantum leaps forward. Everyone else is new. Isaiah Thomas, Avery Bradley, Jae Crowder, Kelly Olynyk, and Amir Johnson have all been replaced by bigger, faster, and more versatile players. Those Celtics were overachievers who emptied their tank to sneak past the Wizards in the second round. This year’s team has lottery picks at almost every position.

Stevens has shifted his lineups several times over the course of the playoffs, but he will likely bench Aron Baynes and move Horford to the 5 to start Brown on LeBron in the Cleveland series. That would put three no. 3 overall picks in their frontcourt (Horford, Brown, and Jayson Tatum), and a no. 6 overall pick (Smart) and no. 16 overall pick (Terry Rozier) in the backcourt. All five are plus athletes for their respective positions, with the defensive versatility to slide around the floor.

Boston exposed Philadelphia’s supporting cast in the second round. The 76ers destroyed the Heat in the first round by surrounding Ben Simmons and Joel Embiid with elite 3-point shooters like J.J. Redick, Marco Belinelli, and Ersan Ilyasova. The Celtics dared Simmons and Embiid to beat them one-on-one, and they ruthlessly hunted those shooters on defense. There aren’t many places to hide a bad defender against Boston: Rozier, Tatum, Smart, and Brown can all attack off the dribble, as can Marcus Morris, their first forward off the bench. Smart is the only one of the five starters who can’t consistently knock down 3s, but he does have the ability to get to the rim and facilitate out of the pick-and-roll.

Tatum and Rozier have stepped up in the playoffs. Tatum is averaging 18.8 points, 4.5 rebounds, and 3.2 assists a game on 45.9 percent shooting. He doesn’t play like a rookie. The game rarely appears too fast for him, and he knows exactly how much space he needs to create to get a shot off, even against elite defenders. The Celtics go from a net rating of plus-6.2 in his 423 minutes in the playoffs, the highest mark on their roster, to a net rating of minus-11.7 in the 163 minutes he sits, by far the lowest. He could have another big series against the Cavs, who don’t have many stoppers on the perimeter.

Rozier will be even more important, especially if Shane Larkin ends up missing time after sitting out Game 5 against Philadelphia with a sprained shoulder. Rozier has emerged as a starting-caliber point guard in the playoffs, averaging 18.2 points a game on 42.3 percent shooting, with an incredible ratio of 5.8 assists to only 1.3 turnovers. Rozier put Eric Bledsoe in a body bag in the Celtics’ first-round victory over Milwaukee, dominating his matchup with the eight-year NBA veteran. Bledsoe is far more explosive than any of the point guards on the Cleveland roster, none of whom have the quickness to keep Rozier in front of them and contest his 3-point shot.

The adjustment Cleveland head coach Tyronn Lue made to slow down Victor Oladipo in the first round was sending multiple defenders at Oladipo in the pick-and-roll to take the ball out of his hands. Boston will have an easier time adjusting to that strategy than either Indiana or Toronto because its center (Horford) is a fluid playmaker who can read the floor and make the right decisions in a four-on-three situation. The Cavs still had an awful defensive rating of 110.1 in their sweep of the Raptors. It just didn’t matter because they had an even more eye-popping offensive rating of 121.5, a massive improvement over the 103.0 they put up against the Pacers.

Kyle Korver played a key role in that resurgence. He went from playing only four minutes in Game 1 against Indiana to averaging 31.5 minutes a game against Toronto. Cleveland unleashed the two-man game between Korver and Kevin Love off the ball in that series, which stretched out the Raptors’ defense and allowed LeBron to conserve some energy. The difference in this series is that every player in the Celtics’ perimeter rotation is a shot-creator, so Korver will have to work on defense. It’s harder to run circles around your opponent when you’re forced to scramble on defense yourself. Stevens could try to play Korver off the floor by closing games with Horford, Morris, Tatum, Brown, and Rozier.

Love also found new life in the second round. He went from averaging 11.4 points a game on 33.3 percent shooting against the Pacers to 20.5 points a game on 47.5 percent shooting against the Raptors. While he had more time to recover after tearing a thumb ligament in Game 2 against Indiana, the biggest difference were the players guarding him. The Pacers used Thaddeus Young, a combo forward with the strength to bang with Love in the post and the quickness to cover him on the perimeter. The Raptors tried either traditional big men (Jonas Valanciunas, Serge Ibaka) who couldn’t track him at the 3-point line or undersized wings (C.J. Miles and DeMar DeRozan) with no chance against him inside.

Raptors head coach Dwane Casey struggled to play the matchup game with Lue, which has been a theme throughout his coaching career. Toronto left a lot of points on the board, and the team still took games 1 and 3 down to the final possession. Cleveland has improved since Lue went back to his veterans toward the end of the Indiana series, but he hasn’t filled all the holes in the lineup. Korver and Love struggle on defense, while Jeff Green and Tristan Thompson are limited offensive players. George Hill and J.R. Smith are their two best perimeter defenders, and they will be giving up a lot of size and speed against Boston.

The gap between the two teams has narrowed considerably from last season. Kyrie Irving is sitting out in street clothes, but his absence is felt more on Cleveland’s bench than Boston’s. Stevens has a lot more options this time around. Thompson destroyed Boston’s undersized big men in 2017, averaging 11.6 points and 7.2 rebounds a game on 73.9 percent shooting. Stevens will likely match Thompson’s minutes with Baynes, who’s built like a rock (6-foot-10 and 260 pounds) and held his own against Embiid in the post in the second round. Casey didn’t try a similar tactic with Valanciunas and Thompson until he was down 3-0. Those are the margins a good coach can eliminate.

Of course, there’s still one thing that hasn’t changed. Like everyone else in the Eastern Conference, the Celtics don’t have an answer for LeBron. They have the perimeter players to theoretically match up with him, but Brown, a second-year player, and Semi Ojeleye, a rookie, are far from finished products on that side of the ball. They were destroyed in the first round by Milwaukee’s supersized wing duo of Giannis Antetokounmpo (25.7 points and 6.3 assists on 57 percent shooting) and Khris Middleton (24.7 points and 3.1 assists on 59.8 percent shooting). LeBron will be even tougher to handle, so the Celtics’ best bet on defense might be to focus on limiting his supporting cast.

Boston is playing with house money. The Celtics have already gone further than anyone could have expected, and they will be a power in the East for a long time to come, regardless of what LeBron does in the offseason. If he heads out West, this series will have been the last opportunity for any team to dethrone him in the Eastern Conference playoffs, where he is 23-0 in postseason series since 2011. Even without Kyrie and Hayward, the Celtics have as much talent this season as any of LeBron’s challengers of the past eight years and significantly more than what Boston had last season. Don’t let what they could become overshadow how good they are already.