Los Angeles, United States — Boston forward Jayson Tatum poured in 40 points as the Celtics beat the Orlando Magic 126-120 on Saturday to improve to 3-0 in the fledgling NBA season while the Philadelphia 76ers fell to 0-3.

The rebuilding San Antonio Spurs stunned the Sixers 114-105 in Philadelphia, where frustrated 76ers coach Doc Rivers said after the game his team was "not ready" to win yet.

In Orlando, Tatum's exploits and a 27-point contribution from guard Derrick White helped the Celtics notch another win in a game that featured 21 lead changes with neither team able to build a double-digit advantage.

Orlando big man Wendell Carter knotted the score at 111-111 with a put-back dunk with 4:23 to play.

Carter then fouled Tatum and Tatum's two free throws ignited a 10-2 scoring run that put Boston up for good.

Terrence Ross led the Magic with 29 points and top draft pick Paolo Banchero added 23, but Orlando fell to 0-3.

That's also where the 76ers found themselves after the inexperienced Spurs — whose championship chances were downplayed by none other than coach Gregg Popovich before the season — drained 16 three-pointers on the way to their second straight win.

Devin Vassell scored 22 points, Keldon Johnson added 21 and Tre Jones chipped in 17 for San Antonio while Doug McDermott made four three-pointers on the way to 14 points.

San Antonio's top-scoring trio all have less than three years experience in the league, and Popovich said he was impressed with the young team's performance on the second night of a road back-to-back.

"What it showed me was they are serious about getting better and knowing what the league is like," Popovich said.

The Spurs withstood a 40-point performance from Philadelphia's star big man Joel Embiid but held James Harden to 12.

"We're not ready yet," Rivers said. "Honestly, we're just not. We're not ready to win yet. You can feel that and so we've got a lot of work to do.

"It's almost like we played these first two games hard, competed, and then felt like 'OK, now we can win some games' — you've still got to go out and earn the game."

In Dallas, Luka Doncic scored 21 of his 32 points in the first quarter and the Mavericks steamrolled the Memphis Grizzlies 137-96 in their home opener.

Ja Morant, coming off a 49-point display against the Houston Rockets, finished with 20 points for the Grizzlies, who were on the back foot from the opening tip-off.

Dallas led by as many as 25 points in the first period and, with the game well in hand, Doncic sat out the fourth quarter.

In Milwaukee, Giannis Antetokounmpo scored 44 points as the Bucks launched a six-game homestand with a dominant 125-105 victory over the Houston Rockets.

The two-time NBA Most Valuable Player was frighteningly efficient in less than 28 minutes on the court, connecting on 17 of his 21 shots from the field, including two of three from three-point range.

The Greek superstar also pulled down 12 rebounds and made eight of 13 free throw attempts, and with 3,508 career free throws overtook Sidney Moncrief (3,505) as the Bucks' all-time leader from the foul line.

Milwaukee opened the game on an 11-0 run and never trailed against a flat Rockets team that fell to 0-3.

In Miami, Jimmy Butler scored 24 points and Max Strus added 20 off the bench as the Heat held off the Toronto Raptors 112-109 in a game that saw a player from each team ejected.

The Heat led by 19 when Toronto's Christian Koloko and Miami's Caleb Martin were ejected with 7:46 left in the third quarter.

They tangled after fighting for a rebound and ended up scuffling in the courtside seats.

The fired-up Raptors then went on a 17-2 scoring run, but Miami held on down the stretch.