Christian Bethancourt tightened things with a two-run blast in the Padres' ninth.
Sardinas wasn't scheduled to play, but he came in at third base after first baseman Stefen Romero was hit by a line drive and left the game with a bruised knee in the fifth.
"That's a tough spot," Mariners manager Scott Servais said. "He has no idea he's even playing today and then, boom, he's in the game and he played really well. His at-bats all day were really good. That's what he can do. He's a talented guy. He's still a very young player, but you kind of saw it all today. He can switch-hit, he's got speed, he can defend multiple positions. It was a good day for him."
New Padres shortstop Alexei Ramirez certainly didn't waste time making an impact in his spring debut. He had an RBI single in the third inning and made a diving play to grab a ground ball hit by Steve Clevenger in the fourth inning.
Seattle starter Nathan Karns, who was making his Cactus debut after being acquired in an offseason trade with the Rays, needed 22 pitches to get through the first inning on Thursday. Karns, who is competing for the fifth spot in the rotation, allowed one hit and a walk in his two innings.
San Diego starter Philip Humber allowed one hit and two walks in two innings. Humber, who tossed a perfect game against the Mariners in 2012, is trying to make the team as a non-roster invitee.
San Diego second baseman Cory Spangenberg had the first hit of the game in the first inning, stole a base and later made a nice diving play to smother a ground ball hit by Mike Baxter, recovering to make the throw to first base.
New Padres pitcher Drew Pomeranz, who could crack the team's rotation or, at the very least, earn a job in the bullpen, struck out two in a scoreless inning.
Romero, who had a homer in Wednesday's victory over San Diego, had a single and a walk. He also robbed Adam Rosales of a hit with a diving catch in right field.
Up next for Mariners: Right-hander Taijuan Walker (11-8, 4.56 ERA in 2015) makes his spring debut on Friday at 12:05 p.m. PT against the Brewers at Maryvale Park. Cody Martin, Mayckol Guaipe, Paul Fry, Adrian Sampson and David Rollins are scheduled to appear in relief. The Mariners' starting outfield trio of Nori Aoki, Leonys Martin and Seth Smith is expected to start after getting Thursday off, while manager Scott Servais will go with backups in the infield.
Up next for Padres: Colin Rea will make his first start of the spring season as the Padres face the Royals on Friday at 6:10 p.m. PT at the Peoria Sports Complex. Rea is a candidate to win one of the final two spots in the starting rotation. He'll be followed by veteran Carlos Villanueva, who is being stretched out this spring as a starter, but could very well end up in the bullpen. The game will be televised live by FOX Sports San Diego and MLB.TV.