Brian Ching scored the only goal of the game in the 13th minute and goalkeeper Pat Onstad made five saves, leading the Dynamo to the quarterfinal round of the CONCACAF Champions League.
With their second win of group play, the Dynamo leapfrogged El Salvador's Firpo in Group B and became the only MLS team to advance out of group play. Although their opponent will not be known until Dec. 10, the Dynamo will host the first match on Feb. 23, 24 or 25.
Thanks to Hurricane Ike postponing the match in September, the Dynamo had a chance to exorcise the proverbial demons more than two weeks after a 3-0 home loss to MLS runner-up New York, ending their bid for a third consecutive league title.
It was a sloppy, hard-fought match that featured eight yellow cards and two red cards.
Wednesday was the Dynamo's 48th competitive match of the season, the most ever in one year for an MLS club, and the team finished the 2008 slate with 19 wins, nine losses and 20 ties in all competitions.
In the opening quarter of the match, the Dynamo controlled play and had several fruitless corner kicks before Ching got the team on the board.
Dwayne De Rosario sent a bending corner kick toward the net, and Ching timed it perfectly, heading a shot toward the top of the goal.
Firpo goalkeeper Juan Jose Gomez was playing a bit too deep and he got a piece of the shot as leapt up. But instead of knocking it away for a save, Gomez just pushed Ching's shot into the net behind the crossbar.
With defender Wade Barrett out of the starting lineup, Ching wore the captain's band Wednesday for the second time this season. The last time he wore it, on May 31 in MLS play against New York, Ching scored the only goal of the game in a 1-0 Dynamo win.
Nate Jaqua, who was selected earlier in the day by Seattle Sounders FC in the 2008 MLS expansion draft, had a good chance in the 35th minute to give Houston a 2-0 lead, but he could not pull the trigger when he had possession at the top of the box.
In the 37th minute, Firpo had their first legitimate scoring chance of the match when Patricio Gomez had a great look from eight yards out against Onstad. Patricio waited on a perfect cross from Christian Sanchez, but Onstad read the play and made the save.
Corey Ashe nearly gave Houston a 2-0 lead in the 40th minute when a tough-angle shot on the far side edge of the box, and De Rosario had a good look in stoppage time, but his laser from 25 feet out was easily swallowed by Gomez.
In their first meeting in San Salvador, the Dynamo struck first and saw Firpo come back in the second half. It was more of the save in Houston, as Onstad was at his best early in the second half when he quashed two quick Firpo scoring chances.
First, in the 54th minute, Fernando Leguizamon fired a quick shot in the middle of the box, but Onstad made the stop.
Two minutes later, it was Leguizamon again. This time, flying down the far side, the Argentinean forward bounced a shot toward the net that Onstad had to dive to his left to stop.
Jaqua's Houston career officially came to an end in the 68th minute when he was replaced by Kei Kamara. Jaqua had four goals and four assists in 14 games with the Dynamo in 2008 after returning to the club from Austria.
Houston had to play most of the last 14 minutes a man down, when defender Eddie Robinson was sent off with a straight red card.
But substitute Carlos Calderon saw a second yellow card of the match in the 91st minute, evening things up, and Firpo was not able to muster another scoring chance in the closing minutes.
Andrew J. Ferraro is a contributor to MLSnet.com. This story was not subject to the approval of Major League Soccer or its clubs.