Two headers granted Sounders an early advantage in the CCL, but Santos' away goal leaves the second leg wide open.
The match set a Sounders FC CCL record with an attendance of 23,433. Four Sounders made their debuts -- Michael Gspurning, Adam Johansson, Marc Burch and Eddie Johnson -- and the referee issued seven yellow cards.
Though no MLS side has won the current incarnation of the Champions League, with three MLS sides in the quarterfinals, one of the storylines this season has been Mexico's relaxed grip on regional dominance.
"We knew the team we were going to face, they are a strong team with a great crowd," Santos coach Benjamin Galindo said. "This team can play with any team in Mexico."
Seattle showed that quickly. Twelve minutes in, Fredy Montero floated a ball above the Santos backline and David Estrada headed home.
"We were planning on moving the ball from side to side really quickly, and that's how the goal came," Alvaro Fernandez said. "That was the plan and we were very successful at the beginning."
The header marked Estrada's first professional goal.
"I'm very happy for him because nobody works harder," Seattle coach Sigi Schmid said of Estrada. "Nobody is more committed than he is. Nobody wants it more. For him to get the goal, to play in this game and to score against Santos Laguna, being a guy who was born in Mexico I think was huge for him."
After an hour former USL Sounder Herculez Gomez equalized. The U.S. international forward flicked a Marc Crosas cross past Gspurning, who made four saves total. Seattle reacted immediately. Brad Evans connected with a Mauro Rosales set piece, using what looked like a combination of his shoulder and neck to loop the ball over Santos goalkeeper Oswaldo Sanchez.
"For a number of weeks now we have been going over set plays and as long as our runs are committed the ball is going to be there," Evans said. "The balls from Mauro [Rosales] are always consistent."
The second leg, in Torreon, Mexico, is scheduled for March 14. Despite the loss, Santos will bank on its valuable away goal.
"I don't think we should be too confident, but we're not that easy to play at home either," Herculez Gomez said. "We have a great fan base and are undefeated at home."
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