TOKYO -- Many of the Mariners' familiar names are gone after an offseason makeover by general manager Jerry Dipoto, but the new crew made its presence felt in a 9-7 win over the A's on Wednesday in the first game of the Opening Series at the Tokyo Dome.

Left fielder Domingo Santana and shortstop Tim Beckham, two of five new position starters acquired over the winter, each blasted home runs and new relievers Cory Gearrin, Zac Rosscup and Hunter Strickland slammed the door with 2 2/3 innings of hitless relief to get the Mariners' season off on the right foot halfway around the world.

Santana quietly went about his business at his first Mariners camp this spring, but the big man made significant noise in his regular-season debut, as his third-inning grand slam ignited the comeback win.

Santana became just the second player in franchise history to hit a slam on Opening Day.

"It feels awesome," Santana said of getting off to a good start with his new team. "Even better, we got a 'W' today, so it feels great."

Beckham, another newcomer, added a two-run shot in the fifth inning in his three-hit day as the Mariners jumped on their American League West rivals in the first game of the Opening Series, the first Major League regular-season action in Tokyo since 2012.

"Certainly the big two-out grand slam by Domingo really gave us a lot of energy in the dugout and we felt good about where were at in the ballgame, but it was really important we continued to add on," manager Scott Servais said. "Tim's home run later in the game proved to be really big. We have to keep put pressure on teams the entire game, and we've got a lineup that can do that this year."

The 6-foot-5, 230-pound Santana hit 30 homers with 85 RBIs in a breakout season for the Brewers in 2017, but he struggled last year and spent much of the season at Triple-A after Milwaukee acquired veteran outfielders Christian Yelich and Lorenzo Cain.

The Mariners love Santana's potential however and acquired him for Ben Gamel to provide some right-handed outfield punch. That pursuit paid off in a hurry with Santana launching his slam in his second at-bat with an opposite-field shot to give Seattle a 5-2 lead.

"He's got a really good swing with power to all fields," said center fielder Mitch Haniger, one of the holdovers who helped secure the win with a key catch up against the wall after the A's had cut the lead to two in the seventh. "He's going to be a really good threat in our lineup. We know we're going to put up runs. With our offense, we can score big in any inning, especially with the power we have one-through-nine."

The 26-year-old from the Dominican Republic led Seattle with four homers in Cactus League play while batting .400 (10-for-25), though his production was somewhat overlooked in a camp with so many newcomers and young prospects sharing the headlines.

Even Wednesday's opener was focused largely on Ichiro Suzuki's return to Japan at age 45, but Santana made sure that party stayed positive by igniting a five-run third off A's starter Mike Fiers. Ichiro wound up going 0-for-1 with a walk before being replaced in the fourth inning.

Marco Gonzales, making his first Opening Day start for Seattle, allowed four runs on seven hits -- including a pair of home runs -- in six innings in a 69-pitch outing.

The A's struck quickly against Seattle's revamped bullpen, with Nick Rumbelow giving up a three-run blast to Matt Chapman in the seventh to cut the lead to 9-7 before Gearrin, Rosscup and Strickland closed things out, with Strickland getting his first save in place of the traded Edwin Diaz.