Houston entered the clash just three points ahead of Portland in the wild card hunt, but with a tremendously tight Eastern Conference, Friday's win helped the Dynamo jump ahead of the Columbus Crew and Sporting Kansas City before MLS action on Saturday.
Andre Hainault gave Houston the lead in the 36th minute before Danny Cruz secured the victory with a brilliant goal in the 59th minute.
Cruz doubled the advantage in spectacular fashion, taking the ball from the right flank and cutting inside before unleashing a shot from distance with his left foot and finding the far upper corner.
Houston is now unbeaten in its last five MLS regular season matches, going 3-0-2 over that stretch. With 46 points on the season and an additional game under their belts, the Dynamo are just one point behind the first-place Philadelphia Union in the East.
Sitting in sixth place in the Western Conference, Portland (11-14-7) is still in playoff contention with 40 points from 32 matches. But the path to the postseason will certainly be difficult, as the Timbers hit the road to face D.C. United, which is also in the playoff hunt, and Real Salt Lake.
Houston (11-9-13) returns home for its final match of the regular season, hosting the Los Angeles Galaxy on Oct. 23.