Houston finished off Philadelphia on Thursday, and the Dynamo are back in a familiar position in the Major League Soccer Cup playoffs.
Brian Ching scored in first-half stoppage time as Houston edged Philadelphia, 1-0, in the second game of their Eastern Conference semifinal series for a 3-1 aggregate victory and a spot in the East final.
Houston (2-0-0) advanced to its fourth conference final in its six seasons in MLS, its first in the East. Houston won consecutive MLS Cup titles in 2006 and 2007, and lost in the conference final in 2009.
The Dynamo will visit Sporting Kansas City, which dispatched the defending MLS Cup champion Colorado Rapids 4-0 on aggregate in their series, on Sunday for a chance to advance to their third MLS Cup in six years.
Philadelphia (0-2-0) rarely threatened to overturn the first-match deficit, a 2-1 home loss, at Robertson Stadium as its first playoff appearance ended with two losses.
Philadelphia remained within a goal into first-half stoppage time, but Houston took complete command of the series when Ching scored on the final play of the first half.
Houston's Brad Davis, who led MLS with 16 assists in the regular season, drove a free kick in from the left wing, and Ching ran onto the ball into the middle of the area and powered a 12-yard header into the top-right corner.
Ching's first goal this postseason - and eighth of his career - gave Houston a 3-1 aggregate lead, and left Philadelphia in need of two goals after halftime just to force overtime.
However, it was Houston that created the best chance to start the second half, as Calen Carr - who scored in the first leg - chested down a field-length pass from goalie Tally Hall at the top of the box only to be denied by a good save.
Carr picked out the lower left, but Union goalie Faryd Mondragon stuck out his foot to deflect the shot wide for a corner. Ching reached another cross from Davis off the corner, but headed wide left to leave the Union hope.
Philadelphia had two chances in the middle of the half to get a goal back, but Veljko Paunovic's well-hit shot from outside the area was held by Hall at the right post in the 59th, and the Dynamo goalkeeper emerged with the ball after a scrum in the area in the 64th.
Hall let out a huge sigh of relief after the second play and, after the Union brought in Freddy Adu, Justin Mapp and Roger Torres in a triple switch in the 66th, the Dynamo continued to lock down their opponents.
Hall was rarely tested as he posted his first shutout of the postseason, after six in the regular season, and Houston extended its undefeated streak to eight games ahead of the one-match Eastern final at Livestrong Sporting Park against Kansas City.