Portland opened the 2015 season with three draws and a defeat to sit bottom on goal difference in the West.
But that all changed at Providence Park in Portland on Saturday as second-half goals from Maximiliano Urruti and Diego Chara lifted the Timbers past Dallas, who lost top spot as a result of their first defeat this season.
Portland climbed to fifth in the standings, four points behind Dallas, who slipped two points off the pace after the in-form Vancouver Whitecaps accounted for reigning champions Los Angeles Galaxy 2-0.
The Timbers and Dallas exchanged goals in the opening half, with Nat Borchers breaking the deadlock for the home side in the 23rd minute, only for Tesho Akindele restore parity six minutes later.
It was one-way traffic after the break as Urruti volleyed the ball past Chris Seitz at the front post in the 62nd minute before Chara sealed the points three minutes from time.
Chicago Fire notched back-to-back wins after upstaging 10-man Toronto FC 3-2 in a thriller at Toyota Park.
Toronto welcomed back international stars Michael Bradley and Jozy Altidore from United States duty but the pair could not prevent the Canadian franchise from crashing to a third consecutive defeat.
The Fire made a dream start in front of their home supporters courtesy of left-back Joevin Jones and his first MLS goal in the 14th minute but Toronto took control from that point as high-profile recruit Sebastian Giovinco opened his account for the visitors six minutes later before Benoit Cheyrou struck in the 54th minute.
Toronto's lead lasted just two minutes after Scotland international Shaun Maloney fired a shot low beyond goalkeeper Joe Bendik.
Warren Creavalle made matters worse for Toronto when he saw red for a second bookable offence in the 67th minute and Chicago captain Jeff Larentowicz capitalised on the home side's numerical advantage 60 seconds later.
Saturday's win saw Chicago jump up to fourth in the Eastern Conference, three points behind leaders DC United and just a solitary point adrift of New England Revolution.
Toronto are third from bottom in the East with one win from four games.
The resurgent Revolution made it consecutive league victories against embattled Colorado Rapids, winning 2-0 on the road.
Juan Agudelo and Lee Nguyen were on target for last season's finalists, who condemned the Rapids to an 18th consecutive match without a win - a joint league record set by Real Salt Lake in 2004-05.
Meanwhile, Obafemi Martins' 39th-minute goal gave 10-man Seattle Sounders a 1-0 victory at home to Houston Dynamo.
