By Ridge Mahoney

The best team during the 2006 regular season and the defending MLS Cup champion face radically different tasks in the second legs of their CONCACAF Champions' Cup quarterfinals Thursday night.

Both are also playing in the Superliga this summer, but could be facing showdowns against Mexican opposition in two weeks.

D.C. United, which cruised to the Supporters' Shield but couldn't get past New England in the playoffs, beat Honduran club Olimpia, 4-1, last week and needs only to avoid a thumping in the home leg (7 p.m. ET, Fox Soccer Channel) at RFK to advance.

Conversely, Houston endured stifling heat, a bizarre penalty-kick call and an even stranger sending-off, a starting goalkeeper lost to injury while allowing a disallowed goal, and a riddled surface better suited to motocross while losing, 1-0, to Puntarenas of Costa Rica in the first leg.

Robertson Stadium is unavailable, so the Dynamo plays the second leg (9 p.m. ET, Fox Soccer Channel) at the Aggie Soccer Stadium on the campus of Texas A&M in College Station, about a two-hour drive from Houston.

D.C. United would be paired with Chivas Guadalajara and Houston against Pachuca in the semifinals should the MLS teams advance. Both Mexican clubs clinched their series last night. The series are decided on total goals and there is no special provision for away goals.

Olimpia, despite the three-goal deficit, could be more than a formality for D.C. Leading 2-1 at the start of the second half, United survived a few scares, including a blast off the crossbar. A second superb goal by Christian Gomez and a very late header from Facundo Erpen ballooned the scoreline.

''It was not a 4-1 game, not even close, and if they score that second goal and it's 2-2 and a whole different ballgame at the start of the second half, and we're in for a pretty long fight,'' says midfielder Ben Olsen. ''They have a lot of talented guys and they're probably going to be fighting for some jobs now, too, 'cause I know they aren't doing that well in the league.''

United also scored just before the first half ended to regain the lead, after Juan Manuel Carcamo's powerful header had tied the game. Although Olimpia failed to dictate the tempo as might be expected from a team playing at home, defender Bobby Boswell believes it still has the potential to cause problems at RFK.

''They're going to come out firing,'' says Boswell. ''If we can weather that storm and if we can keep them off the scoreboard and maybe even get an early one, it'll break their spirit and make our day a lot easier.''

Houston coach Dominic Kinnear isn't anticipating anything being easy for his team. He's short a few key players and needs to revive a sluggish attack. A rough, bumpy field in Costa Rica neutralized Dwayne DeRosario and Brad Davis, and a team normally among the best conditioned in the league wilted in the second half.

''The heat killed us,'' says Kinnear. ''That and losing Eddie [Robinson]. We were already under the gun a little bit and then we have to play with 10 men, which makes the job twice as hard.''

Starting keeper Pat Onstad suffered a calf injury in the first leg and is out, though stand-in Zach Wells saved a penalty kick and was only beaten in stoppage time by a deflection off the foot of a most unlucky Ricardo Clark.

''He was upset with the goal and I thought he was being hard on himself,'' says Kinnear of Wells, who was acquired last year from the then-MetroStars but didn't play in any MLS games.

Also out is Robinson, suspended with a second yellow-card. Forward Brian Ching could see some time, but he's still recovering from offseason surgery and isn't likely to start.

''We're being very careful with Brian,'' says Kinnear of his rugged forward who scored 11 goals in just 21 games last year. ''It's going to be long season, with all these competitions we're in and national team games. He'll probably see some time, depending on how the game goes.''

The first-leg festivities included a slice of tragicomedy; team trainer Bruce Morgan, frustrated at not being allowed on the field to treat a limping Alejandro Moreno, barked at the officials and was ordered off by referee German Arrendondo. Morgan is expected back for the second leg.

''Giving up the goal was heartbreaking but if you look at everything we had to go through, we only lost 1-0,'' says Kinnear, ''so playing at home we have a great chance.''

Quarterfinals, 2nd leg
Thursday, March 1
D.C. United (MLS) vs. Olimpia (Honduras) (agg.: 4-1)
TV: Fox Soccer Channel (live) 7 pm ET/4 pm PT.
Fox Sports en Espanol (delay) 2:30 am ET/11:30 pm PT.

March 1
Houston (MLS) vs. Punterenas (Costa Rica) (agg: 0-1)
TV: Thursday, Fox Soccer Channel (live) 9 pm ET/6 pm PT.
Fox Sports en Espanol (delay) 11:30 pm ET/8:30 pm PT.

Feb. 28
Pachuca (Mexico) 1 Marquense (Guatemala) 0 (Pachuca advances, 3-0, on aggregate)
Luis Angel Landin hit the winner.

Feb. 28
Chivas Guadalajara (Mexico) 3 W Connection FC 0 (Chivas advances, 4-2, on aggregate).
Sergio Santana scored twice for Chivas and Adolfo Bautista scored the third.