Five yellow cards and three goals, all before halftime.

Such was the case last night when the Union opened the first leg of its two-game playoff series against Houston at PPL Park.

In the 16-year history of the MLS, an average of 2.2 goals have been scored in tightly contested playoff matches, and in this affair three found the back of the net in the first half.

However, the score line didn't end favorably for Philly, as Houston took the first match, 2-1, courtesy of a gritty Calen Carr game-winner in the 30th minute. And that was unfortunate for the crowd of 18,539 that included Flyers stars James van Riemsdyk and Scott Hartnell and Phillies free-agent shortstop Jimmy Rollins serving as honorary captains.

The decision gave Houston its first-ever win against a Union side that matched the physical intensity of the Dynamo, but still could not avoid silly fouls and now crucial cautions. For the game, the Union drew four yellows and Houston two.

Houston hosts the pivotal finale on Thursday (8:30 p.m., ESPN2). The club with the most goals on aggregate will advance to the Eastern Conference final to be held either Nov. 5 or Nov. 6 against the winner in the other conference semifinal between Sporting Kansas City-Colorado. Houston is ahead 2-1 on aggregate, meaning ideally the Union needs to hold Houston scoreless Thursday and score a pair to advance. A daunting task for a team that has scored more than one goal just seven times in MLS matches all year. Should the match be tied 2-2 on aggregate (meaning Union is ahead by one goal Thursday), then two 15-minute overtimes will commence. Should the score line remain the same, then the match goes to penalty-kick shootout.

Houston struck first just 5 minutes in after a Brad Davis free kick found defender Andrew Hainault. The goal came after Union defender Gabriel Farfan landed a yellow-card caution for going studs up to the face of Houston's Danny Cruz. Two minutes later, the Union brought it level when true-footed forward Sebastien Le Toux brought down a ball inside from Michael Farfan in the 18-yard-box just above the six and slotted the equalizer near post past goalkeeper Tally Hall, playing in his first playoff match.

Not sure if it was cold gloves on a frigid night, but Hall looked shaky in his first outing, unable to keep a firm grasp on balls directed to the low posts and corners. However the Union neglected to take advantage of that, as far too many shots were directed right at him.

Four Union players are under a dreaded yellow-card caution. Along with Farfan, midfielders Stefani Miglioranzi and Brian Carroll and defender Sheanon Williams could potentially miss the conference final on Nov. 5 or Nov. 6 with another caution.

Defensively, the Union went with a five-man front in the final third as Miglioranzi helped out the customary four of Williams, Gabe Farfan, Carlos Valdes and Danny Califf. It proved effective as Houston appeared shaky on the counter and had little defense against speedsters Le Toux and Danny Mwanga, who didn't seem slowed by the hip injury he has labored with for two-thirds of the season.

The second half found goal-scoring chances arriving in waves, with the ball hitting the crossbar twice off shots from second-half substitutes Freddy Adu and Jack McInerney. But following a seasonlong trend, the Union's inability to finish key opportunities came back to haunt them, fittingly on Halloween eve.