Calvin Natt scored 21 of his 28 points in the second half to help beat Philadelphia in Portland.
The loss ended the 76ers' six-game winning streak and was only their second in the last 22 games.
Rookie guard Lafayette Lever preserved the victory with three steals in the last four minutes, the last coming with 35 seconds to go and Philadelphia trailing by four.
The 76ers, playing their fifth game in seven days, were was sluggish at the start, then rallied behind Moses Malone to take the lead in the opening minutes of the third quarter. But they could never stretch the margin beyond two.
Kenny Carr scored 14 of his 20 points in the third quarter as the Blazers rebuilt an 80-72 lead. Carr's final field goal was a 55-foot bank shot at the third-quarter buzzer.
The 76ers closed to 94-92 with 4:52 left, but the Blazers scored eight straight and Lever had two steals in the next 1 1/2 minutes.
Malone paced Philadelphia, which had 22 turnovers, with 28 points and 15 rebounds. Julius Erving added 25. Mychal Thompson had 25 points and 12 rebounds for Portland.
There were four technical fouls and 57 personals in the rough contest.