CenturyLink Field will be packed to the brim on Sunday as Seattle Sounders FC plays host to the Portland Timbers in Clint Dempsey's first taste of Cascadia Cup action.

Dempsey has made two appearances since joining Seattle from Tottenham, both of which have come on the road.

And in order to accommodate the bump in attendance that will accompany Dempsey's first home match in the famed green Sounders kit, the club has opened CenturyLink Field to full capacity by allowing for 66,500 seats to be filled.

"I knew there was a chance, but now we are really selling the tickets," goalkeeper Michael Gspurning told a correspondent from the club's official website. "It's just awesome to play in front of this crowd."

Seattle is 7-0-2 all-time in matches that draw crowds over 40,000 and has won all four matches played in front of over 55,000, holding an 11-1 scoring edge.

The Sounders had a three-match winning run snapped last time out as they suffered a 3-1 loss to the Houston Dynamo, but Portland is without defeat in three league outings, most recently finishing with a point in a 3-3 draw with Real Salt Lake on Wednesday.

The Timbers appeared to have the three points all sewn up when Kalif Alhassan netted a go-ahead goal in the 86th minute, but Cole Grossman scored in stoppage time to see the two sides split the points.

"Well, if we're being honest, I think we're all pretty gutted not to get that three points," said head coach Caleb Porter. "Obviously, it's in our hands, 3-2. We did a heck of a job in that second half, battling back ... In the end, we're disappointed, but we don't have time to be too disappointed.

"We have a big game on Sunday. I told the guys there's some things we need to address, but mostly we need to put it behind us quickly and get to work on Seattle. We can't have a hangover in this tight of a window. Psychologically we need to move on quickly, get ready for Seattle."

Portland enters the weekend on 39 points, three points back of first-place Salt Lake and five points better than the seventh-place Sounders.