The win marked Portland's highest scoring performance of the season as well as their second time in the last six matches of scoring four or more goals. They moved up three spots into fifth place in the Western Conference with the win.
Carlos Fierro scored the lone goal for San Jose, which suffered its second-worst defeat of the season after a 7-1 loss to the Seattle Sounders on Sept. 10. The Earthquakes had managed two draws between those defeats but are now winless in their last seven matches and remain last in the West.
The Timbers took the lead in the 25th minute after a somewhat unfortunate bounce for the Quakes, when a bouncing ball struck San Jose defender Shea Salinas in the arm for a clear handball.
Referee Rosendo Mendoza pointed to the penalty spot, and Valeri stepped up and drove a low finish into the left corner past Daniel Vega's dive.
Portland doubled its lead only two minutes later. A San Jose defender cleared away the initial cross from a free kick from the right. The ball cycled to Jorge Villafana on the opposite flank, who drove in a second cross toward the back post, where Ebobisse met it with a powerful header past Vega.
Fierro pulled the Quakes back within one just before halftime. Marcos Lopez dragged a cross from the left back toward the top of the penalty area, and Fierro hit a first-time, left-footed shot past Aljaz Ivacic and inside the right post.
But Valeri's second goal 12 minutes after halftime, on a one-time strike of Yimmi Chara's cross, began a cascade of four unanswered goals for the visitors.
Chara's goal made it 4-1 in the 70th minute, Cascante headed in Valeri's free kick in the 85th and Niezgoda completed an attack set up by Diego Chara in the 87th.