With a berth in the NBA championship finals on the line in the best-of-seven series, J.R. Smith set a Cavaliers club record for three-pointers, draining eight from beyond the arc.
His 28 points accounted for all of the scoring by Cleveland reserves.
“I was just trying, if anything, to take good shots,” Smith said. “I got in a rhythm early and just stayed aggressive.”
Smith’s long-range bombs came in bunches, including three in the first two minutes of the fourth quarter as he helped Cleveland build an 18-point lead.
He broke James’s prior Cavaliers record for three-pointers in a playoff game by one. James made three against Washington in game four of the 2006 Eastern conference quarter-finals.
“Those who know J.R. know when he gets hot, he gets smoking hot,” said Cavaliers coach David Blatt.
“He was terrific. Probably overlooked is how well he defended and that he got eight rebounds.”
Four-time NBA Most Valuable Player James scored 31 points, pulled down eight rebounds and handed out six assists for the Cavaliers.
He said defence was the key to the victory.
“We’re the number one defensive team in the playoffs. In order for us to win, ultimately we have to defend,” said James, who is playing in his fifth straight Eastern Conference finals after four appearances with Miami.
“Tonight we shot 44 percent from the field, but we defended. We gave ourselves a chance. When you defend at a high level you’re going to give yourself a chance to win every night.”
James has won two titles with the Heat and returned to his home state and first NBA team the Cavaliers, vowing to bring Cleveland a championship.
He sealed Wednesday’s victory with a thundering dunk in the final minute.
Tristan Thompson added 14 points and 10 rebounds in the win and Kyrie Irving had 10 points and six assists in 27 minutes.
Jeff Teague scored 27 points to lead Atlanta, but the Hawks lost starting forward DeMarre Carroll to a left leg injury in the fourth quarter.
Carroll, who appeared to hyperextend his left knee when he planted his foot to take a shot, crumpled to the floor in pain.
Rival James gave him some encouraging pats as Hawks personnel helped him from the court.
“At the end of the day, we’re all a brotherhood,” James said. “You never want anyone to get injured, even in combat.”
Hawks coach Mike Budenholzer said Carroll would have an MRI exam on Thursday to assess the severity of the injury.
“At this point, I think the doctors are saying it’s a knee sprain,” Budenholzer said. “We’ll know tomorrow.”
The Cavaliers will try to strengthen their grip on the series in game two on Friday.
The winners of the series will take on the Western Conference champions in the NBA Finals.
Golden State, the best team in the regular season, leads Houston 1-0 in the Western Conference championships.