The Galaxy (9-2-9) extended their unbeaten streak to 11 games in front of a sellout crowd of 27,000. They lead the MLS with 36 points and haven't lost since May 1.
Perk was in the lineup for the first time since being claimed off waivers last season from Philadelphia. He had only seen action in reserve matches and tournament play before the start.
"Tonight, he looked like a guy who has played before," Galaxy coach Bruce Arena said. "He's a keeper we can put in there and know he can be successful."
Perk was called into action with starter Donovan Ricketts out because of a broken left forearm and Josh Saunders serving a suspension. The second-year goalkeeper blocked Fredy Montero's penalty shot in the 18th minute, diving to his right for his first career save.
Perk said he experienced some nervousness before the game, but settled in once he made the key save.
"After that, I was fine. I was in the groove," he said. "There were a couple back passes I need to do better on. But other than that, pretty solid."
It was the first save on a penalty kick by a Los Angeles goalie since July 16, 2009.
"They're a good team," Sounders goalie Kasey Keller said of the Galaxy. "They have the most points in the league, and there's a reason for that. We came here and gave them a good game."
The Sounders (8-4-8) had their three-game winning streak halted, but they matched a club record with their seventh straight game without a loss.
Juan Pablo Angel had a pair of chances from close range that could have put the Galaxy on top, including a shot in the 68th that hit the foot of the goalpost.
"A draw was probably a fair result," Keller said. "But at the same time, either team could have stolen it."
The Galaxy lost a pair of defenders to injuries in this one. A.J DeLaGarza left the field on a stretcher in the first half with a head injury and Omar Gonzalez suffered a left hip pointer late in the game.
Arena said he expects both to be fine and ready for the team's next match on July 9.
David Beckham was not in the starting lineup, but entered as a substitute and played 22 minutes. It was his first action in three games because of a slight stress fracture in his lower spine.
Los Angeles and Seattle will meet again next week in the quarterfinals of the U.S. Open Cup.