The Celtics flexed their muscles at home Monday to earn a 117-101 Game 1 win over the 76ers in the Eastern Conference semifinals.

Boston, playing without shooting guard Jaylen Brown, who was ruled out minutes before the game, had three players step up in his absence. The Celtics are also obviously still missing Kyrie Irving and Gordon Hayward, who are out the rest of the season.

Al Horford helped guide the young Celtics with 26 points and seven rebounds. Rookie Jayson Tatum added 28 points, and point guard Terry Rozier caught fire from beyond the arc (7 of 9), scoring 29 points with eight rebounds and six assists.

Here are three takeaways from the Celtics' win:

1. Next man up policy working for Celtics — Injuries have plagued this elite team all season, but it's never really seemed to bother them. The Celtics have lost the likes of Hayward, Irving, Marcus Smart and most recently Brown to injuries, forcing them to change their tactics. But every time someone goes down, someone else steps up.

Despite all the losses, Boston continues to score and shoot at a proficient rate. Injuries are never fun for coaches, but Brad Stevens has to be pleased with the way some of his younger players have stepped up this season when called upon.

2. 76ers still have some growing up to do — Joel Embiid is a monster on both ends of the court. The agile center scored 31 points with 13 rebounds Monday, but the young 76ers still have something missing. Ben Simmons scored 18 points with seven rebounds and six assists, and J.J. Redick added 20 points. Still, several of Philadelphia's impact players failed to contribute in Game 1.

Guys like Dario Saric, Robert Covington and Markelle Fultz (who did not play because of coach's decision) will ultimately need to become more consistent for this team to reach full potential. It could happen this series. It could never happen. That's what makes the 76ers so exciting right now.

3. Defense still lives in the NBA — It can be a little difficult trying to sit through some regular season NBA games. Guys just stand around as guards drive through the lane unopposed and dunk. But the Celtics played tough defense all season, and that's continued into the playoffs.

Boston held the 76ers to just 42.2 percent shooting Monday, and just 19 percent from 3-point range. Tatum and Horford are great on-the-ball defenders, and Rozier has developed into a dangerous two-way player. If the Celtics continue to lock down on defense they may be hard to beat leading up to the NBA Finals.