For the 29th player on a 28-man roster, José Marmolejos made quite an impact for the Mariners on Thursday.

After being added as the allowed “extra player” for a doubleheader, Marmolejos launched two home runs after replacing injured first baseman Evan White midway through the first game at Petco Park in San Diego, including a grand slam in an 8-3 victory in Game 2.

• Box score

The 27-year-old rookie also ripped a two-run shot in Seattle’s 10-7 loss in the opener and wound up 3-for-7 with the two homers, a double and six RBIs on the day.

“When we needed a big hit, Marmo got us going with the grand slam,” manager Scott Servais said. “It was great to see from a guy who, when he woke up this morning, had no idea he was going to be on the active roster. He ends up hitting two home runs for us. It was a big day for him, and a lot of guys contributed.”

Marmolejos made the Opening Day roster after signing with Seattle as a non-roster invitee on a Minor League deal after nine years in the Nationals’ system. But he hit just .103 (3-for-29) with a home run in eight games and wound up back at the alternate training site for the past three weeks.

The Mariners brought him on this seven-game road trip as part of their five-man taxi squad in case they needed to add a left-handed bat due to injury or illness. What they didn’t expect was that the team wouldn't play on Wednesday as a statement in support of racial equality around the country in the wake of the Jacob Blake shooting in Kenosha, Wis.

• Servais: 'We need change'

That resulted in Thursday’s doubleheader -- and the ability to add a 29th player -- and Servais chose to activate Marmolejos with the thought he could come off the bench or perhaps fill in at designated hitter in the second game.

“I found out when I was walking toward the field at around 9 or 10 this morning,” Marmolejos said. “I got a text from Skip, and I just said, ‘Thank you very much. I really appreciated it.’”

But instead of a bench role, he wound up inserted at first base in the fourth inning of the opener after White injured his right shoulder, and wound up doing damage all day.

Marmolejos became just the fifth Mariner in franchise history to hit home runs in both games of a doubleheader, joining Alex Rodriguez (2000), Edgar Martinez (‘99), David Segui (‘98) and Jay Buhner (‘90).

The 6-foot-2, 240-pounder highlighted Seattle’s six-run first inning in the second game with his 421-foot blast off Padres starter Garrett Richards, who also allowed a solo shot by Shed Long Jr. before his day ended following just two outs.

Marmolejos added a double in the seventh inning of the finale and also turned a key double play in the sixth. On reliever Joey Gerber’s first pitch in relief after Aaron Fletcher loaded the bases with one out, Marmolejos stepped on first and then threw home to get Seattle out of a jam.

“That’s a pretty impactful 29th man,” said Servais. “We might have to keep him around a little longer. He really swung the bat well today. I’m really happy for him.”

Marmolejos said the biggest adjustment he made after being sent to the alternate training site was simply relaxing and not pressuring himself so much.

“I was really thankful I got brought back,” he said. “But at the same time, I was just taking it easy and taking it pitch to pitch and enjoying the game. That was one of the things that I learned. I got all nervous and wasn’t enjoying the game like I used to.”

The Mariners had plenty to enjoy in the second game, as they wound up taking two of three in the series from a Padres team that entered on a seven-game win streak and is in second place in the National League West.

“I was really proud of our guys to bounce back after a really tough first game,” Servais said. “This was one of those days where everybody needs to chip in, and everybody gets a chance to play. You look at this series, I thought we played really good baseball. We had one bad inning, otherwise we might have walked out of here with a sweep against a really good team.”

Yusei Kikuchi (1-2, 6.12 ERA) picked up his first win of the season after allowing three runs on seven hits over five innings with six strikeouts in an 81-pitch outing.