Terrence Ross scored 19 points, Landry Fields had 14 and the Toronto Raptors beat Boston 99-97 on Wednesday night, handing the Celtics their fifth loss in six preseason games.
MarShon Brooks scored 17 points, 15 of them in the final quarter, and Kelly Olynyk fouled out with 13 points and nine rebounds for the Celtics.
Boston had a chance to tie it on the final possession, but Jared Sullinger couldn't tip in Jordan Crawford's missed 3-pointer.
Vitor Faverani and Jeff Green each scored 13 for the Celtics, who were coming off an 82-80 loss to former teammate Paul Pierce and the Brooklyn Nets on Tuesday.
Kyle Lowry scored 11 points and Rudy Gay and Jonas Valanciunas each had 10 for the Raptors, who won their third straight and improved to 4-1 in the preseason.