With Hisashi Iwakuma yet to throw this spring because of an injured right middle finger that will be in a splint for another three weeks, and Taijuan Walker shut down for at least a week with shoulder inflammation, the Mariners are leaning on Paxton to claim a rotation spot.
The left-hander struck out Nick Hundley on a high fastball. Third baseman Willie Bloomquist's two fine defensive plays helped in a 19-pitch outing.
"It's early in the spring but the young man has talent," Mariners manager Lloyd McClendon said. "He's capable of doing things. He pounded the zone down and that was pretty impressive."
Paxton acknowledged knowing he needed to provide the staff with a boost.
"Definitely, it's great to go out there and do that," he said. "Those guys will be back quick. They're working hard and I'm sure they're going to be back really soon."
Nick Franklin homered for the Mariners off Tim Stauffer. Nate Tenbrink and James Jones also homered and Seattle had 18 hits.
Most of the Mariners' regulars, including Robinson Cano, had the afternoon off.
Andrew Cashner threw two scoreless innings and new Padres setup man Joaquin Benoit gave up one hit in a scoreless inning.
Ryan Jackson doubled and scored for the Padres, who have committed six errors in two games.
Mariners: Paxton, who went 3-0 with a 1.50 ERA in four September starts following his first big league call-up, was sharp and confident as he worked on his fastball and cutter. He said he threw one curveball.
"Trying to pick up where I left off last year," he said. "Really just focusing on executing pitches right now and getting everything refined."
Padres: Cashner struck out Ty Kelly and Corey Hart on changeups to get out of a first-inning jam.
Cashner, who led the Padres with a 3.09 ERA last year, gave up one hit and 18 of his 32 pitchers were strikes. He didn't throw any breaking balls.
"I felt like I was a little jumpy out there in the first inning, the ball was up a little bit," he said. "But I thought for the most part I did what I wanted to do: work the fastball both sides of the plate."
Mariners: The team announced Walker would be shut down for a week with shoulder inflammation before the game, then after the game revealed Iwakuma is still at least three weeks away from throwing.
"Of the guys who are pitching right now, it's good for us to get out there and show we're not hurt," Paxton said.
Padres: Third baseman Chase Headley played catch Friday morning, the next step in his recovery from a strained right calf.
"He's doing well," manager Bud Black said.
Headley, who still hasn't been cleared to hit, is expected to sit out at least a couple more weeks of games.
Black said right-hander Keyvius Sampson (groin) is expected to pitch in a game this weekend.
Benoit, signed to a two-year, $15.5 million deal in the offseason, struck out one and had an effective changeup in his San Diego debut.
"I still have to work a little bit on my mechanics," he said. "I was a little too quick to the plate."
Joe Wieland struggled in his first appearance after missing all of last season following reconstructive elbow surgery. He allowed four runs on four hits, including a homer, while getting two outs.
"I thought his fastball was fine," Black said. "He hung two breaking balls."