Portland fell behind 32-11 in the first quarter and trailed the entire game on their way to a 102-94 loss in Boston to open a three-game road trip Monday night.
The Blazers went almost five minutes before hitting their first field goal of the game, and Boston raced out to a 21-7 lead with 3:52 left in the first period.
Portland trailed by double digits most of the way but did climb to within eight points on a Caleb Love layup in the final minute of the third quarter.
Jerami Grant scored on a layup and Tamari Camara hit a pair of free throws to shrink the gap to 99-94 with 0:42 to play, but that was as close as the Blazers would get.
Grant came off the bench to lead Portland with 19 points, while Camara scored 18. Deni Avdija sat out Monday night.
Payton Pritchard out of West Linn led the Celtics with 23 points on 5-of-11 (45.5%) shooting from 3-point range.
The Blazers (23-24) play at Washington at 4 p.m. Tuesday.