Tatum, back at full fitness after missing most of last season with a ruptured Achilles, delivered a mesmerizing performance at the TD Garden to give Boston their first win of the campaign after an opening-day loss to Detroit.
The six-time NBA All-Star shot 14-of-26 from the field, including three three-pointers, with nine rebounds, seven assists and three steals.
Nine of Tatum's points came in the fourth quarter as the Knicks, who had trailed by as many as 12 points early in the final frame, closed to within one point.
Tatum's superb all-round display earned words of admiration from Celtics coach Joe Mazzulla.
"That was a really well-balanced game from JT on both ends, and you were able to kind of see his greatness," Mazzulla said after the home opener.
Tatum received scoring support from new signing Paul George and Neemius Queta, who both finished with 15 points apiece.
The Knicks were led by 22 points from Karl-Anthony Towns, with OG Anunoby and Miles McBride scoring 20 each. Knicks talisman Jalen Brunson chipped in with 19.
The Toronto Raptors made the biggest move of the NBA off-season when they acquired franchise icon Kawhi Leonard in a trade, and early on, the move is paying off big as the team moved to 2-0 with another win on Friday night. The star of the show in this one however was Scottie Barnes, who led the Raptors with 28 points and 14 rebounds, with 23 from RJ Barrett putting four of their five starters in double digits on the night.
With the loss, the Wizards move to 1-1 on the season, with Trae Young providing the spark as he posted 22 points and 12 assists on the night, and with a healthy Anthony Davis and a young core, this is a team that could clearly make some noise in 2026/27.
In other NBA action on Friday, the Minnesota Timberwolves stayed unbeaten with a 115-93 defeat of the Orlando Magic on the road.
Minnesota's new-look offense, with Anthony Edwards and LaMelo Ball working in tandem, produced a balanced scoring display that saw seven players finish in double figures.
Edwards and Jaden McDaniels each netted 15 points to top the scoring. Orlando fell to 0-2 with the loss.
Elsewhere, the Atlanta Hawks moved to 2-0 with a 128-81 drubbing of the Charlotte Hornets, with Jalen Johnson and Aaron Wiggins scoring 19 points each.
In defeat, Naz Reid was fantastic with 17 points and 6 rebounds, but given the Hawks depth and defensive versatility, it just wasn't enough for a Hornets team still looking to find their identity after taking a major step forward in 2026/27.
Kyrie Irving's 24-point haul helped the Dallas Mavericks to a 121-105 defeat of the Indiana Pacers, with the returning Tyrese Haliburton quickly finding his strides once again, but with the team making some changes, it's going to take some time for them to find their consistency.
In support of Irving, the Mavericks got 20 points from PJ Washington as the team had six players in double digits, with an 18-6-7 night not enough to keep this one close for Haliburton and the Pacers at home as both teams move to 1-1 early in the year.
Early in the day, the Milwaukee Bucks were left waiting for their first win of the campaign as they were taken down by an under-the-radar Chicago Bulls team, led by a combined 46 points from Norman Powell and Caleb Wilson, picking up the 132-125 victory.
With their two-time MVP traded in the off-season, the Bucks didn't lack for offense in this one as Tyler Herro's 34 points led all scorers, with seven players in double digits including all five starters not enough to get it done as they officially start the year 0-2.