WASHINGTON -- D.C. United faced a tall order over the weekend, needing a victory against the league-leading Columbus Crew in order to keep pace in the tight race for one of the final MLS Cup Playoff berths.The Black-and-Red got the job done, slogging their way to a 1-0 win in cold, wet conditions to give themselves hope going into their season finale at Kansas City on Saturday."The team showed a real commitment to working hard and defending, which you need to do at this stage in the season," said head coach Tom Soehn afterwards. "Obviously everybody knows the importance of the game in keeping our playoff hopes alive. The guys grinded one out and gave everything they had."But the magnitude of that task pales in comparison to what Soehn's men will face on Tuesday night in Toluca, high in Mexico's Sierra Nevada mountains some 40 miles southwest of Mexico City. United face Group B leaders Deportivo Toluca in their final CONCACAF Champions League group stage match that night, needing a win to guarantee passage to the tournament's quarterfinal rounds.Winning on Mexican soil is an achievement no MLS club has ever reached, however -- and that history of futility is matched by the U.S. national team's struggles against their southern neighbors, with a range of factors conspiring to make life exceedingly difficult for each and every U.S. side that ventures south of the Rio Grande.Beyond the wealth, depth and overall quality of the Mexican Primera Division, draining travel itineraries and hostile crowds must also be factored into the equation and to top it off, many of the destinations in question are located at lung-busting altitude.Toluca offers a particularly acute challenge in this regard. The city sits some 8,750 feet above sea level, comparable to the Colorado mountain town of Telluride and significantly higher than Denver and Commerce City, home to the Colorado Rapids, where visiting MLS teams routinely suffer in the rarified air -- United, for example, have not won a road match against Colorado since 1999.United have endured several heartbreaking losses in Mexico over the years, narrowly losing to Chivas de Guadalajara and Pachuca in CONCACAF and Copa Sudamerica play, and they were well beaten in their first Champions League match against Toluca, a 3-1 setback at RFK on August 26. A draw or even a loss on Tuesday could still see D.C. through to the knockout rounds, but those results would depend on CD Marathon failing to garner full points against Group B stragglers San Juan Jabloteh when the Honduran side visits Port of Spain, Trinidad on Thursday night.Toluca has been dominant in Champions League play at Estadio Nemesio Diaz, scoring 10 goals and allowing none in one-sided victories against Marathon and Jabloteh. So United would be expected to take a defensive posture on Tuesday -- except that the squad has spent the past two weeks working on an aggressive 3-5-2 formation designed to seize the initiative against Columbus.That approach was abandoned in favor of a more conservative 4-4-2 shape when the Crew pushed forward in search of an equalizer, however. Toluca's attacking quality will further shrink the margins for error in the D.C. defense, making tactical acumen a central aspect of United's upset hopes."We tried to play down the lanes and that kind of stretched the field and gave us enough space so when we played inside we could get shots and guys could dribble more, because there's more space on the field when the strikers check and run," said center back Julius James after Saturday's win. "So we kept the defense honest. When we were up, they put the pressure on so we went to 4-4-2 to hold it down."Soehn and his team flew out of Washington before dawn on Monday morning, leaving several mainstays like Clyde Simms, Jaime Moreno and Ben Olsen behind with an eye towards Saturday's crucial league match in Kansas. So the MLS playoff hunt looms large in United minds -- and given the circumstances, a positive result in Toluca would surely rank among the most impressive feats in the capital club's distinguished history.