RSL turned in a tremendous performance at Rio Tinto Stadium, but a late Portland goal took some of the gloss off the win heading into the second leg.
After the visitors struck first through Will Johnson, RSL hit back with four unanswered goals, before substitute Frédéric Piquionne scored what could be a vital goal for Portland right before the final whistle.
Just 14 minutes into the contest, the visitors struck out ahead. Johnson lined up a 25-yard free kick just right of center, and his scorching strike sent Nick Rimando to his left initially, and he couldn't recover in time as the ball flew into the far post.
With 10 minutes left in the first half, RSL drew level. Javier Morales whipped in a corner kick and Chris Schuler – scorer of the extra-time goal that put his team in the conference final – rose up above Futty Danso and nodded home to the far post.
Danso was again negatively involved as RSL took the lead five minutes later. A long clearance was completely misplayed by the center back, allowing Robbie Findley to steal in and slot home past Donovan Ricketts to give his side the lead.
Things would get even better for the home side right after the break, as RSL doubled the lead. A quick counter sprung Findley down the right flank, and the forward crossed low towards Devon Sandoval. The rookie was composed in taking a touch at the six yard line before finishing low to the far post.
RSL would get a killer fourth goal with 10 minutes remaining. Javier Morales made a near-post run off a corner kick, and his header took a slight deflection before it rolled under Ricketts.
Just as it appeared the home side would travel to Portland with a three-goal lead, the away side grabbed what could be a vital goal at the death. Jack Jewsbury sent a hopeful ball to the far post, where Piquionne rose up and sent a perfect header into the opposite corner, giving his team a huge lifeline heading into the second leg on Nov. 25.