The crowd of 67,385 trailed only the first home game for the Los Angeles Galaxy against New York in 1996 that drew 69,255. It topped the 66,452 that saw Seattle and Portland play last October at CenturyLink Field and was the largest for any match in Seattle, topping a friendly against Manchester United in 2011.
Johnson scored his fourth goal against the Timbers moments after his speed in the open field drew a free kick when he was chopped down by defender Pa Modou Kah. Mauro Rosales' curling ball into the box found Johnson wide open after he left defender Alvas Powell behind.
It was Johnson's sixth goal in MLS play. Seattle improved to 35-0-8 in its last 43 games when scoring first and controlled the second half after Portland had the better chances in the first 45 minutes.
More importantly, the Sounders moved into a tie for fifth place in the Western Conference with 37 points and still have at least one game in hand on the rest of their playoff competition.
Seattle was on pace for another crowd of 60,000-plus before Dempsey's arrival. But the acquisition of the U.S. captain from Tottenham, plus Seattle's archrival being his first home match, pushed the stadium past its capacity.
Before the game, fans jammed Occidental Park north of the stadium for the annual pregame march to it. Flares were lit, songs were sung and full city blocks were crammed with fans in rave green.
And No. 2 jerseys with "Dempsey" across the back flooded the stadium.
Dempsey received the loudest screams when he was the last name announced during pregame introductions. Fans added Dempsey-related signs around the stadium, including "Dempseyland" on north stands.
He delighted the fans with his footwork and creativity. In the first half, he flicked a no-look pass to Johnson and nearly scored in the second-half on a modified scissor kick as he tried to get his first goal for Seattle.
The Timbers weren't afraid to be physical with Dempsey, pushing him off the ball when they could. Kah was especially willing, drawing Dempsey's ire and a few shoves in the back. But it was his careless tackle on Johnson that led to the free kick that gave Seattle the victory.
Portland had its chances to ruin the night for its rivals to the north, with multiple scoring chances in the first half and a few in the second half. Portland's Darlington Nagbe had a shot from outside the box that was punched over the net by goalkeeper Michael Gspurning in the 88th minute. Andrew Jean-Baptiste's header was caught by Gspurning in stoppage time.
Gspurning was also forced to make a number of key saves in the first half, coming off his line to smother Ryan Johnson on a breakaway in the 16th minute and getting a bit of luck in the 37th minute when Diego Valeri's shot from outside the box curled but his the goalpost flush and ricocheted away.