The Sounders host freshman club the Timbers at Qwest Field on Saturday and general manager Adrian Hanauer is expecting a fairly large turnout.
When asked by the Seattle Times if they would attract a crowd of 50,000, Hanauer was only slightly optimistic about that number but confident of a strong attendance.
"Maybe. I really don't know. My gut doesn't tell me that there are tens of thousands of people that are out there who don't feel like they can get a ticket to our games when they want," he said.
"We just know from how many season tickets we've sold, when we sell out each game, and how far in advance. This Portland game didn't sell out immediately, so that tells me that maybe there aren't tens of thousands of people out there pining that they weren't able to get a ticket for this. But I don't know."
He also said that it should prove to be the start of a great rivalry between two fairly new clubs on the MLS scene whose competition dates back to the USL days.
"Obviously it's very exciting from a rivalry standpoint and the energy around this big game coming up against Portland," he added.
"My strongest memories are from the USL days because I was in the thick of it and there were just some unbelievably good games here at Starfire, tough battles, and thankfully we got the best of them a lot of the times. Those Open Cup games down there the past couple of years have been special as well."