Jaylen Brown had 23 points and eight rebounds, and Marcus Morris added 21 points and 10 boards as the Boston Celtics stunned the LeBron James-led Cleveland Cavaliers 108-83 in Game 1 of the Eastern Conference finals Sunday.
Al Horford finished with 20 points and six assists, and Jayson Tatum scored 16 for the undermanned Celtics, who reached the East finals without injured stars Kyrie Irving and Gordon Hayward.
"I just try to lead 'em the best way that I can and really lead by example," Horford told the ABC broadcast about the Celtics' young roster after the game. "We're just out here playing hard and having fun."
James totaled 15 points, nine assists and seven rebounds as the Cavaliers' five-game playoff winning streak ended. Kevin Love led the Cavs with 17 points and grabbed eight rebounds. Rodney Hood added 11 points and Jordan Clarkson had 10.
Game 2 is Tuesday night in Boston.
"Just as confident going into a series no matter if it's a 0-0 series or if I'm down 0-1," James said. "We have another opportunity to be better as a ballclub, come in Tuesday night and we'll see what happens."
Cleveland swept the Toronto Raptors and Boston beat the Philadelphia 76ers in five games to set up a rematch of last year's East finals. James and the Cavaliers eliminated the Celtics in a five-game series last May.
"Last year we came off of a grueling, seven-game series against Washington," Horford said. "One day rest, we had to play Cleveland. You give them credit -- they were the better team.
"This year, we were able to close the series out with Philadelphia, have a couple days. I feel like the coaches came out with a great game plan for our group, and you know we just bought in and did what we were supposed to do."
James has appeared in seven consecutive NBA Finals series, including three straight with Cleveland. Boston is seeking its first Finals berth since 2010, when it lost in seven games to the Los Angeles Lakers.
Boston shot 51.2 percent (43 of 84) from the field and 36.7 percent (11 of 30) from 3-point range while outrebounding the visitors 48-40. Cleveland was held to 36 percent shooting (31 of 86) from the floor.
JR Smith's buzzer-beating jumper had the Cavaliers within 78-64 after three quarters, but a Tatum finger roll put the Boston lead over 20 at 85-64 with 10:52 remaining. Cleveland trailed by as many as 29 after that.
The Celtics were up 61-35 at halftime. Brown's 3-pointer with 32.4 seconds left in the second quarter gave Boston its biggest lead of the half at 61-33. The Cavaliers never came closer than 15 in the period.
Boston led 36-18 after one quarter after going up by as many as 21, matching the biggest first-quarter deficit James has ever faced in a playoff game. Boston went on a 17-0 run midway through the period.
Celtics reserve Shane Larkin (left shoulder sprain) did not play. Larkin is already ruled out for Game 2 and is likely to miss the entire series. Boston started Morris in place of Aron Baynes to match up against James.