Teams that sit back against Guadalajara are often punished, and the team's tepid league performance to date has thrown this competition to the forefront.
"It's going to be a very difficult game," said striker Luciano Emilio, who leads MLS with 20 goals, on mlsnet.com. "We can't go in thinking we have any kind of advantage. We have to go in thinking the game is 0-0, which it is. That's the type of mentality we need to have success."
When the teams met in the CONCACAF Champions Cup six months ago, United played rather tentatively at home in the first leg and escaped with a 1-1 tie. A more aggressive approach in the return leg caught Guadalajara off-guard, but United conceded a couple of soft goals and lost, 2-1.
Since then, Guadalajara has lost in the semifinals of the Torneo Clausura to its bitterest rival, Club America, and to Pachuca in the CONCACAF Champions Cup finals. It started badly enough in the Apertura that two days after losing the first Copa Sudamericana match at RFK, team management fired Coach Jose Manuel de la Torre.
With replacement Efrain Flores in charge, it beat Veracruz, 3-1, Sunday in a league match at Jalisco. Alberto Medina, Ramon Morales and Sergio Santana -- who assisted on Medina's goal -- scored to wipe out an early 1-0 deficit.
D.C., too, rallied to win its league match, blasting Toronto, 4-1, Saturday with four goals in 18 minutes after falling behind in the first half.
United's sharp form over the past two months - its only losses have come against MLS teams in the SuperLiga - and good showings against Club America (1-0) and Morelia (1-1) are reasons for optimism it can advance to face Argentine club Arsenal in the quarterfinals.
A sluggish first half against Toronto prompted Coach Tom Soehn to bring Ben Olsen and Jaime Moreno off the bench at halftime rather than resting them to face Guadalajara.
Defender Bryan Namoff, who suffered a thigh contusion against Guadalajara in the first leg, sat out against TFC but is expected to be available for the second leg.
United got goals from Olsen and Clyde Simms in the first leg yet struggled to contain Santana, who scored Guadalajara's goal, and allowed Medina a few clear chances as it was outshot, 21-5 while playing the entire second half a man down following Marc Burch's second caution.
Despite substitutions and tactical tweaking, United seldom looked solid in defense, and without shoring up its resilience for the second leg will face a very long night.