Marcus Smart scored 12 points off the bench, including a 3-pointer during an 8-0 Boston run to start the fourth quarter, and the Celtics pulled away for a 118-95 victory over the host New York Knicks on Saturday night.
Kemba Walker had a game-high 32 points, a majority of them on seven made 3-pointers, as the Celtics overcame a horrible start to sweep a back-to-back sequence that began with a home win over Toronto on Friday.
RJ Barrett went for 26 points for the Knicks, who lost their home opener after tipping off the season with a pair of defeats on the road.
Barrett and Julius Randle combined for 12 points when the Knicks, coming off a 113-109 loss at Brooklyn on Friday night, blitzed the Celtics early with a 16-4 run to open the game.
But Boston dominated most of the rest of the action, building an 82-76 lead by the end of the third quarter and then pulling away quickly in the final period.
Grant Williams converted a Jaylen Brown pass into an alley-oop dunk, Carsen Edwards hit a jumper and Jayson Tatum converted a free throw when ex-Celtic Marcus Morris was assessed a technical foul as they combined with Smart for the fourth-quarter-opening run that ballooned Boston's lead to 90-76.
The Knicks got no closer than nine the rest of the way.
Smart's key 3-pointer was one of three he hit in the game. Brown (19 points), Tatum (15) and Edwards (10) also scored in double figures for Boston, which outscored New York 45-21 on 3s.
Randle had the game's only double-double with 10 points and 10 rebounds for the Knicks. Mitchell Robinson had 17 points and Morris 12 for New York.
Bobby Portis led all rebounders with 11 off the bench for the Knicks, who outrebounded Boston 55-45.
Tatum was the Celtics' top rebounder with nine.