Josh Jackson also had 13 points for the Raptors. Siakam recorded six rebounds and Achiuwa seven boards as the Raptors improved to 2-0 in the preseason.
Jaylen Brown led the Celtics with 23 points and Sam Hauser had 22, connecting on 8 of 12 shots, including 5 of 8 from outside the arc. Jayson Tatum finished with 18 points and 10 rebounds for Boston, now 1-1 in the preseason.
Payton Pritchard scored 17 points and had five assists
The teams were tied at 110 at the end of regulation after Jeff Dowtin (10 points) converted a 9-footer for the Raptors. Pritchard’s 18-footer was off the mark as time in regulation ran out, sending the game to the extra period.
The Raptors outscored the Celtics 11-4 to open overtime and never relinquished the lead.
Joel Embiid and James Harden were done with their preseason debuts long before Montrezl Harrell scored the go-ahead basket with 26 seconds left, and the Philadelphia 76ers beat Cleveland 113-112 in Donovan Mitchell's first game with the Cavaliers.
Embiid had 12 points and six rebounds in 18 minutes before taking a seat after halftime. Harden played 19 minutes and scored nine points, going 3 of 9 from the field but adding five assists.
Tyrese Maxey, who had 20 points in Monday’s win over the Nets, continued his good start to the preseason, leading Philadelphia with 21 points in the first half. He went 9 of 11, making all three of his 3-pointers. Harrell, who signed a two-year contract with Philadelphia during the offseason, scored 13 points.
Cleveland played without second-year big man Evan Mobley, who is expected to be out a couple of weeks with a right ankle sprain suffered this week.
The Cavaliers got an optimistic glimpse of the backcourt tandem of Mitchell with Garland in the first half. Mitchell was 6 of 9 for the game, including 3 of 4 from outside the arc to go with five assists. Garland, meanwhile, made 4 of 7 shots and handed out four assists.
Shake Milton had 12 points for Philadelphia, while De’Anthony Melton, picked up from Memphis in a draft night trade, had 11 points, four rebounds and three assists.
DOC UNDER THE WEATHER
Doc Rivers was absent from the game with an undisclosed illness. Assistant coach Dave Joerger, who has head coaching experience with the Grizzlies and the Kings, ran the club.
PACERS 122; HORNETS 97
Aaron Nesmith scored 16 points, rookie Benedict Mathurin, the No. 6 pick in the draft from Arizona, added 15 and Indiana beat Charlotte.
Isaiah Jackson finished with 13 points for the Hornets, while Myles Turner and Chris Duarte contributed 12 points apiece. Mathurin was 5 of 10 from the field, despite missing all four of his 3-pointers over 19 minutes.
Terry Rozier led the Hornets with 18 points and P.J. Washington finished with 13. Kelly Oubre Jr. had 11 points and nine rebounds, while LeMelo Ball scored 12 points and handed out seven assists.
MAVERICKS 98; THUNDER 96
Dwight Powell finished with 13 points and five rebounds for the Mavericks in their opening game of the preseason.
Josh Giddey led the Thunder with 13 points, shooting 6 for 10. Rookie Jalen Williams, the 12th overall pick out of Santa Clara, finished with 10 points.
The Associated Press