The resilient Celtics, despite losing two of their top players to injury, are headed to the Eastern Conference finals of the NBA playoffs against the LeBron James-led Cavaliers. Game 1 in the best-of-seven series takes place Sunday at TD Garden (3:30 p.m. ET).

The Cavaliers are 1.5-point favorites, with the over-under for total points scored set at 203.5.

For the best analysis on this matchup, listen to SportsLine senior analyst Larry Hartstein. The veteran handicapper had another strong NBA season, which he has built on with a 16-7 record in against-the-spread picks during this season's playoffs.

Moreover, he's been right on the pulse of these clubs, as he is on an 8-2 run in spread picks involving the Cavaliers or Celtics. Anyone who has followed him is way up. Now, Hartstein has broken down Game 1 and isolated a huge X Factor that determines the outcome. He's sharing what it is, and what side to back, at SportsLine.

Both clubs have faced their share of adversity and skeptics on their way to meeting with a trip to the NBA Finals on the line.

The second-seeded Celtics limped into the playoffs with stars Kyrie Irving and Gordon Hayward shelved with injuries. They needed seven games to outlast the Bucks in the first round, but then stunned the rising 76ers in five games.

Fourth-seeded Cleveland took a somewhat similar path. The Cavaliers were beset by roster turnover, inconsistency and their own injury issues all season. They were pushed to the brink of elimination by the Pacers in the first round.

In a somewhat stunning about-face, James and friends rekindled their longstanding dominance over the Raptors and knocked the top seed out of the postseason in a four-game sweep.

Will the Celtics dominate again on their home court, or will the Cavaliers make a statement with a road victory and cover? Visit SportsLine now to see which side of Cavaliers-Celtics is a must-back, all from a seasoned handicapper on a 16-7 NBA run.