Much of the club's success the past two years is rooted in a knack of knowing when to play it cozy, when to lock up the storm windows, and when to push down on the pedal.
Houston stormed forth from the second half kickoff and broke the deadlock with a Dwayne DeRosario goal 50 seconds in, then scored two more in bang-bang succession before conceding a late goal to win, 3-1.
Houston moves onto the semifinals to face either Deportivo Saprissa or Atlante. Their series, which Atlante leads, 2-1, after its home leg, concludes with the second leg Thursday.
The Dynamo hosts the semifinals, first leg April 2, and the return leg is scheduled for April 9.
Mario Rodriguez broke through the Houston defense twice during a first half controlled periodically by the Guatemalan team, but he boomed his first attempt over the crossbar and with his second chance couldn't jam the ball past Dynamo keeper Pat Onstad after breaching the back four.
From the second-half kickoff, Houston won a throw in the Municipal half, and DeRosario dribbled in from the left wing and ran down a scuffed clearance, perhaps cushioning it with the upper portion of his arm, before firing the ball past keeper Jaime Penedo.
The incident sparked sharp protests from the Municipal players and as it turned out, the controversy and acrimony regarding use of the upper appendages were just getting started.
DeRosario netted a penalty midway through the second half after referee Mauricio Morales blew his whistle for a foul by Claudio Abizures, who apparently clipped Corey Ashe's heel as they dueled for a ball in the box. Protests ensued, then DeRosario slammed home the penalty past keeper Jaime Penedo.
A fracas broke out shortly after the restart and two players from each team were cautioned. The Guatemalans were still bickering when midfielder Ashe highlighted a Man of the Match performance by running onto a great diagonal ball from Brian Ching to center a pass that Chris Wondolowski tapped into the net in the 73rd minute.
Houston should have played it cozy, or perhaps locked it up tight, but Municipal charged forth to regain some of its first-half momentum. Not until the 86th minute could it break through; former Galaxy attacker Guillermo "Pando" Ramirez tucked away a penalty kick after Wade Barrett's forearm blocked a cross.
Just a few minutes later, Rodriguez headed a cross at goal from close range and Onstad watched anxiously as it nicked the outside of the post. Early in stoppage time, Carlos Figueroa shot wide from a good position. Municipal attacked again and Rodriguez rolled a shot into the net, but Morales waved it off for yet another handball, this time on Rodriguez, whose protest prompted Morales to brandish the yellow once again.