Perez made it 2-0 with his solo shot in the fourth inning, and the Royals manufactured another run in the fifth when Billy Butler sent an RBI grounder through the left side of the infield.
That was all Seattle starter Erasmo Ramirez allowed in 6 1-3 innings. After getting recalled from Triple-A Tacoma, Ramirez scattered seven hits and three walks while striking out three.
"I made a couple of pitches in the game, like the homer to Perez," he said. "That happens."
Bruce Chen was just as stingy for the Royals early in the game.
The soft-tossing left-hander allowed four weak singles through the first five innings before Franklin Gutierrez ripped a crisp base hit to lead off the sixth. Seager followed with his home run to right field, which cleared the visiting bullpen and landed deep in the seats.
Seattle tied the game up in the seventh inning. Royals reliever Kelvin Herrera gave up a pair of singles, and Brad Miller's groundout off relief pitcher Tim Collins knotted the game 3-all.
The Mariners threatened again when they put runners on second and third with one out against Collins in the eighth inning. Hochevar struck out Mike Zunino and got Chavez on a fly ball to center to end the inning, and walked off the field to a standing ovation.
"We got some hits tonight," Seager said. "It's just kind of the same thing. They were able to make some good pitches and get out of a couple of jams."
Notes: The Mariners added LHP James Paxton, RHP Chance Ruffin, RHP Hector Noesi and INF Carlos Triunfel from Triple-A Tacoma before the game. They also added Triple-A hitting coach Howard Johnson to the staff. ... The Royals added RHPs Wade Davis and Louis Coleman from Class-A Wilmington, and LHP Donnie Joseph and INFs Johnny Giavotella, Pedro Ciriaco and Carlos Pena from Triple-A Omaha before the game. ... RHP Taijuan Walker starts for the Mariners on Wednesday. RHP Ervin Santana goes for KC.