Stephen Curry scored 42 points for the champions, while Kevin Durant added 25 as the Warriors overcame a markedly changed side to the one they defeated for the title in June.
Cleveland lost talisman LeBron James over the summer as a free agent, while All-Star Kevin Love is out through injury.
Oklahoma City Thunder's narrow 114-112 win over the Brooklyn Nets all came down to an incredible fourth quarter from Paul George.
He scored 25 points in the final quarter alone, sending his game total to 47, and grabbed the deciding three-pointer that lifted his side over Brooklyn with just 3.1 seconds to go.
In the night's other games, Jamal Murray scored 31 as the Denver Nuggets beat the Orlando Magic 124-118 and Karl-Anthony Towns scored 35 as the Minnesota Timberwolves stung the Charlotte Hornets 121-104.
The Los Angeles Lakers beat the San Antonio Spurs 121-113, the Dallas Mavericks were defeated by the New Orleans Pelicans 132-106 and the Detroit Pistons were shut down by the Milwaukee Bucks 115-92.
The Philadelphia 76ers lost to the Toronto Raptors 113-102 and the Los Angeles Clippers were beaten by the Memphis Grizzlies 96-86, while the Washington Wizards saw off the Atlanta Hawks 131-117.