Boston entered the NBA season on a high but it took less than six minutes for them to crash when their All-Star recruit Gordon Hayward dislocated his ankle and fractured his leg in a sickening fall.
The NBA guaranteed plenty of drama and plot lines when they pitted the Celtics against rivals Cleveland in Tuesday's opening game of the season and it ended up being a thriller.
There was also late drama in the second of the games on the opening day of the 2017/2018 campaign, with Houston getting the win against Golden State after Kevin Durant's buzzer-beater proved to have come too late.
The Cavaliers staved off the Celtics 102-99 in the earlier of the two games.
It began in nightmare fashion when Hayward climbed high for an alley-oop pass from the Celtics' other off-season All-Star recruit, Kyrie Irving, midway through the first quarter.
Hayward collided in the air with LeBron James and crashed to the floor on his left leg in a horrifying way.
"My thoughts and prayers go out to Gordon," James said
"It was a pretty gruesome injury."
A hush fell over Cleveland's home arena as players grimaced, including the Celtics' Australian big man Aron Baynes, as Hayward winced on the floor and team doctors set the foot back in place.
There was plenty of bad blood entering the game.
James and Irving had been teammates on the championship-winning Cavaliers, but Irving fled to the Celtics in the off-season to partner with Hayward who left the Utah Jazz and signed a four-year, $128 million ($A163 million) contract.
The injury will almost certainly end Hayward's season.
Baynes played with aggression in his first game with the Celtics, challenging James at the rim, and contributed six points, five rebounds and one block in 19 minutes.
James fell just short of a triple double with 29 points, 16 rebounds and nine assists while Irving had 22 points and 10 assists.
In Oakland, Golden State were presented with their championship rings for beating Cleveland in last season's finals series.
Nick Young top scored for the Warriors with 23 points, as Steph Curry added 22 and Kevin Durant 20, but it was the points Durant didn't score which proved to be the big story.
The forward appeared to have stolen the game with a mid-range jumper on the buzzer, but replays showed time had expired before the ball left his hands, giving Houston the 122-121 win.
James Harden scored a game-high 27 points and was well supported by Eric Gordon (24 points) and PJ Tucker (20 points) off the bench.
Rockets recruit Chris Paul managed four points, eight rebounds and 11 assists in his regular season debut for Houston.
