Associated Press

SAN DIEGO — Rookie José Marmolejos had a pretty good day for a guy who didn’t know he was on the roster until three hours before the first pitch of Thursday’s doubleheader.

Marmolejos hit his first grand slam and Shed Long Jr. also connected in the six-run first inning that carried the Seattle Mariners to an 8-3 victory against the San Diego Padres and a doubleheader split.

Marmolejos also had a big defensive play at first base and had two home runs on the day.

“When we needed a big hit, Marmo got us going with a grand slam in the first inning,” manager Scott Servais said. “It was great to see from a guy who, when he woke up this morning, had no idea he’d be on the active roster and he ended up hitting two home runs for us.”

The Mariners took two of three from the Padres, who got three home runs Thursday from red-hot Manny Machado.

In the first game, San Diego’s Wil Myers hit a game-ending three-run homer to cap a seven-run rally with two outs in the seventh inning to stun the Mariners 10-7. Machado had two homers among his three hits and drove in four runs.

They played the doubleheader after the Mariners voted unanimously not to play Wednesday night as a protest of the shooting of Jacob Blake in Kenosha, Wisconsin. The Mariners have the most Blacks in baseball, eight on the active roster and 11 on the 40-man roster.

The Mariners jumped all over Garrett Richards (1-2) in the first inning of the second game. Marmolejos, added as the “29th” player for the doubleheader, hit his grand slam with one out and Long connected with two outs to give Seattle a 6-0 lead and chase Richards. It was Marmolejos’ third and Long’s second.

“I wasn’t thinking about a grand slam, I was just thinking about solid contact,” Marmolejos said. “He knew it was gone “as soon as I hit it. Sometimes you know that feeling. I was grateful.”

Marmolejos also homered in the first game.

Machado homered in the bottom of the first off Yusei Kikuchi (1-2), his 11th. The Padres continued to cut into the lead on Jurickson Profar’s RBI single in the second and Trent Grisham’s RBI single in the fifth. That scored Jorge Mateo, aboard on his first career hit, a ground-rule double.

San Diego loaded the bases with one out in the sixth but the rally fizzled when pinch-hitter Josh Naylor grounded out to Marmolejos at first, who threw out Eric Hosmer at home.

Seattle added two runs off David Bednar in the seventh.

Marmolejos said he was walking to the ballpark about three hours before first pitch when he got a text from Servais that he was on active roster. “I just said, ‘Thank you very much. I appreciate it.’”

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

Overall, “Wow, what a day of baseball,” Servais said. “This is a crazy game. Heck of a response by our team. Very proud of the guys after a really tough loss in the first game to bounce back with the big inning.”

Richards has had two straight short outings.

“I think I’m nibbling a little bit right now instead of just kind of trusting my ball in the zone,” he said. “I feel like a letdown right now. I feel like I’ve put the bullpen in a crippling situation moving into Colorado. There’s a lot of things that kind of go across my mind right now, but the beauty of it is I’ll get another chance in five days.

“I don’t want to be the guy in the rotation that is a question mark.”

In the first game, San Diego rallied from a 7-3 deficit to stun the Mariners.

Myers watched for a few seconds as his majestic shot sailed well over the left-field fence, tossed his bat and pointed to the Padres’ dugout in one motion, and then began his trot. He tossed off his helmet as he approached home and leaped onto the plate and into as wild a celebration.

“That was a lot of fun,” Myers said. “I made the last out the last inning and was able to do something there that inning right there. Just all around offensively that last inning was really cool. We never gave up. Down to our last out and we come around and do that. It was really cool all the way around with the win.”

After Craig Stammen allowed four runs in the top of the seventh, Seattle’s Taylor Williams (0-1) gave it right back in the bottom of the inning. He gave up a two-run, bases loaded single to Machado. Another run scored on a wild pitch and Eric Hosmer tied it with an RBI single.

Dan Altavilla came on and allowed rookie Jake Cronenworth’s single before Myers homered to left, his eighth.

Pierce Johnson (3-1) got the win.

Austin Hedges started the winning rally when he was hit by a pitch, and Trent Grisham and Fernando Tatis Jr. drew walks, “and then we just went barrel to barrel to barrel and you get it to Wil and you’re sitting there first and third and he laid off a pitch and then he got something he could handle,” Tingler said.

Servais called it “about as a crazy a last inning that you’re going to see in a ballgame in quite some time. We weren’t able to close it out.”

The Padres had tied the game 3-3 with impressive home runs by Fernando Tatis Jr. and Machado opening the sixth inning. Tatis hit his big league-leading 13th homer an estimated at 448 feet onto the roof of the Western Metal Supply Co. Building in the left-field corner at Petco Park, making him just the second Padres player to homer to the top of the landmark.

Machado followed with a shot into the second deck in left field, his second of the game and ninth this season. Both were off Matt Magill.

Ljay Newsome pitched four strong innings in his first big league start about three hours after the Mariners announced scheduled starter Taijuan Walker had been traded to Toronto.

Newsome, making his second big league appearance, retired the first seven Padres batters and 10 of 11 before Machado homered to left-center with one out in the fourth, his ninth. Newsome allowed three hits, struck out four and walked none.

The Mariners took a 3-0 lead off Dinelson Lamet in the fourth, including Marmolejos’ two-run homer to left-center.