Jaylen Brown scored 23 points and the Celtics withstood a 42-point night by LeBron James to beat the Cavaliers 107-94 and take a 2-0 lead in the Eastern Conference finals.
Terry Rozier added 18 points, while Al Horford finished with 15 points and 10 rebounds.
Boston improved to 8-0 this post-season at TD Garden. The Celtics have never blown a 2-0 series lead in the playoffs.
James added 12 assists and 10 rebounds. He scored 21 of Cleveland's 27 points in the first quarter , tying his playoff career high for points in a period.
His 42 points marked his fifth 40-point game of this post-season.