The win marked the Blazers' first four-game winning streak of the season.
Wallace gave Portland the lead for good, 96-93, with a shot from the arc with 2:54 left in the extra period. The edge was 96-95 when Wallace stole the ball from Antonio Davis and threw down an alley-oop dunk off a feed from Damon Stoudamire with 1:21 remaining.
"We can't say enough about Rasheed's play lately," Portland coach Maurice Cheeks said. "His aggressive play has been a big factor. He has the ability to take our team to a higher level."
Zach Randolph scored 20 points and Stoudamire added 10, a season-high 14 assists and seven rebounds for Portland, which has won five of six after a three-game losing streak.