Pascal Siakam sank the game-winning 3-pointer in overtime, propelling the Indiana Pacers to a thrilling 135-132 victory over the Boston Celtics on Wednesday, marking the defending champions' first loss of the season.
This rematch of last season's Eastern Conference finals leaves the Cleveland Cavaliers as the sole unbeaten team in the East.
Despite a warm welcome for Bronny James, the Cavaliers cruised to a dominant 134-110 win against the Los Angeles Lakers, improving to 5-0.
In Indianapolis, Bennedict Mathurin shone with 30 points and 11 rebounds, while Siakam added 29, and Tyrese Haliburton contributed 17 points along with 12 assists. The Pacers held a commanding 24-point lead early in the third quarter.
Boston outscored Indiana 38-24 in the fourth, twice cutting the deficit to three before Jayson Tatum drained a step-back 3-pointer with 14.4 seconds remaining in regulation.
Boston took its first lead since the first quarter on Derrick White's driving layup that made it 132-130 with 39.7 seconds left.
But Siakam had the last word, making a basket to tie it, then rising for a three-pointer over Haliburton with 7.3 seconds to play.
"It's big, it's big," Siakam said. "We lost a couple of games because of turnovers and rebounds. So we wanted to get this one."
Tatum scored 37 points, Jaylen Brown added 25, and White scored 23 for Boston, but they couldn't pull off the comeback.
"We let them come back, but I thought we fought," Siakam said. "That's what we've got to do. We've got to be a team that fights to the end."
Boston dropped to 4-1 as Cleveland improved to 5-0 for just the third time in franchise history.
Wednesday's game was billed as a homecoming for LeBron and Bronny James, who hadn't played since being subbed in to play alongside his superstar father in the Lakers' season-opening victory over the Minnesota Timberwolves. That made them the first father-son duo to play alongside each other in an NBA game.
This time around, LeBron James had departed for good, and the game was out of hand when Bronny James was subbed in late in the fourth quarter, receiving cheers from Cleveland fans who remembered him as a toddler attending Cavs games when his father starred for his hometown team.
Turnovers cost Lakers
Although the 20-year-old drafted by the Lakers in June is expected to be headed to the developmental G League soon, he did hit a mid-range jump shot for his first NBA points.
"To see him get his first NBA basket in this arena, where he grew up not too far from here, it's an unbelievable moment," LeBron James said.
Nevertheless, it will be little consolation for the Lakers.
The Cavs made 17 three-pointers to the Lakers' six and turned 21 Lakers turnovers into 31 points.
Cleveland took control with a red-hot first quarter, connecting on 77.3% of their shots from the field.
The Cavs led by 19 at halftime, and turnovers doomed the Lakers' efforts to make significant inroads in the third.
Evan Mobley scored 25 points, and Donovan Mitchell added 24 as six Cavs players scored in double figures.
LeBron James led the Lakers with 26 points. Anthony Davis added 22 points and 13 rebounds, but Los Angeles dropped its second straight game.
The Oklahoma City Thunder remained unbeaten in the West, improving to 4-0 with a 105-93 victory over the San Antonio Spurs.
Luguentz Dort scored 20 points and Chet Holmgren added 19 for Oklahoma City as San Antonio star Victor Wembanyama was held to six points on 1-of-5 shooting.
Wembanyama added eight rebounds and three blocks, but it was Holmgren who came out on top in their matchup of second-year big men.
Elsewhere, Karl-Anthony Towns erupted for 44 points and 13 rebounds to propel the New York Knicks to a 116-107 victory over the Miami Heat.
Jaden Ivey scored 23 points, and Cade Cunningham added 22 to lead the Detroit Pistons to their first win, a 105-95 triumph in Philadelphia, where the 76ers continued to struggle with stars Joel Embiid and Paul George sidelined by injury.