TOKYO -- For much of 2018, the A's relied on a deep lineup and a bullish bullpen to mask a weak rotation, a fickle formula that resulted in 97 wins and an unexpected playoff appearance. The club's decision-makers were consequently conservative in their offseason approach, hoping the same system works again.

They brought back Mike Fiers on a two-year deal, banked on a bounce-back campaign from the newly signed Marco Estrada and took another chance on Brett Anderson, a veteran trio that's expected to carry the load for this staff.

Fiers' struggles were too much to overcome in their 2019 debut, however, and the A's were saddled with a 9-7 loss to the Mariners within the confines of a boisterous Tokyo Dome on Wednesday.

The good news: Oakland's lineup still packs a powerful punch, even halfway around the world. Homers from Stephen Piscotty, Khris Davis and Matt Chapman accounted for six runs in the eventful affair.

"It's good to see the offense come and just play the kind of game we are used to playing, where sometimes we're a little behind but we just keep chipping away," Chapman said. "I think we have a lot to take away from this game, especially early in the season. First game there's always those jitters, but I thought we settled in well and I like where we're at."

Seattle, though, also came out swinging, getting a grand slam from Domingo Santana in the third off Fiers, who needed 36 pitches to get through the inning -- his last. The right-hander's first career Opening Day start fizzled fast; after he faced just one over the minimum through the first two innings, Fiers walked two and hit a batter in a five-run third that erased Oakland's 2-0 lead.

"A lot of pitches, a lot of deep counts and one big hit from Domingo kind of got me there," Fiers said. "I just needed to make a pitch and get out of the inning and not let them put up a number like that. It definitely hurts. I make a pitch and get out of the inning, who knows what happens? But we came out swinging, and it's just kind of tough for me to give the lead back like that."

The Mariners kept at it against Oakland's bullpen, getting a run off Liam Hendriks in the fourth and three more in the fifth, two coming on Tim Beckham's two-run homer opposite Ryan Dull for a 9-4 advantage. Both issued leadoff walks that turned into runs.

"That's probably the one thing I'm most frustrated with, just putting the guy on right away and then putting us up against the wall," Dull said. "I completely felt like I did two years ago all spring, and then just having it go completely different the first night, it's not how I drew it up to be."

The homer-happy A's didn't go quietly, though. Chapman greeted reliever Nick Rumbelow with a three-run homer in the seventh, bringing about thoughts of the many magical moments that were had in the later innings of 2018.

"We always feel we have a chance to come back, and we get to 9-7, we feel pretty good, but they shut us down," A's manager Bob Melvin said.

"We pride ourselves on never counting ourselves out of any game no matter where it's at," Chapman said. "We treat every at-bat the same, and I think that's why we've been able to pull out those late wins. We showed we still have that fight and are not going to get complacent. We're always battling and that's a good testament to our team."

Piscotty collected baseball's first long ball of the season with a solo shot in the first inning, and Davis, who led the Majors with 48 homers last year, got his first one out of the way in quick fashion. The A's slugger swatted a two-run shot to center field in the third inning against Seattle lefty Marco Gonzales.

"They're swinging the bats well," Fiers said. "It's our job as pitchers to set the tone and go deep in the game. I put us in a hole pretty early and we used a bunch of the bullpen. It's just not a good job by me."