Seattle's pitching has allowed just one run and six hits in the first two games, but it was the offense that created the buzz in this one as Morse continued what the Mariners started this spring while thumping a club-record 58 home runs in Cactus League play.
"It's good," Morse said. "I don't think anybody is playing over their abilities. Guys are comfortable up there. We had a good spring and I think it's carrying over. We're just playing good baseball."
It's just the eighth time in the Mariners' 37-year history they've opened a season with two straight wins, and they've done so against an Oakland team that won the American League West last year and topped Seattle in their last seven meetings of 2012.
Morse drove a three-run blast to the opposite field with two out in the third, clearing the right-field fence and a leaping Josh Reddick for his first home run for the Mariners since 2005. He added his second with a monster solo shot to dead center in the ninth.
"It's a difference-maker in a ballgame right there," manager Eric Wedge said of Morse's first home run, which turned a 1-0 deficit into a game the Mariners never trailed the rest of the way. "It changes the entire course of the ballgame. Everything changes, the way you manage, the whole mindset in the entire ballpark and both clubs."
Though Morse played in the Seattle organization from 2004-08, he hit just three home runs in 300 at-bats over 107 games while spending much of that time in the Minors. Only after he was traded to the Nationals in 2009 did he emerge as a power threat, hitting 31 homers in 2011 and 64 total in his past three seasons.
After being reacquired in a trade from the Nationals, the 6-foot-5, 245-pounder hit a club record nine home runs this spring, the most of any Major Leaguer, and continued that power display with Tuesday's blasts.
The Mariners haven't had many legitimate power threats in recent seasons, with no player totaling more than 20 homers in a season since Russell Branyan hit 31 in 2009.
"Anytime you can add a guy like him, that's big," said third baseman Kyle Seager. "You saw what he could do tonight. He can take over a game with one swing of the bat. That was a big knock to get us going in the third and obviously what he did in the ninth was pretty special.
"He's just got that [feeling] where anytime he goes up to the plate, you never know ... something like that can happen. And that's pretty special."
Kendrys Morales, the Mariners' other major middle-of-the-order offseason addition, drove in his first run of the season with an RBI single in the fifth for a 4-1 lead.
The Mariners got production from some of their returners as well, with Seager going 3-for-3 with two doubles, two walks, two runs and an RBI.
First baseman Justin Smoak went 0-for-3, but drew two walks, the second one driving in a run with the bases loaded in the seventh to make it 5-1. Michael Saunders stole two bases and scored a pair of runs from the leadoff spot.
The Mariners worked six A's pitchers for eight walks, including three in the seventh along with a hit batter.
Iwakuma was outstanding in his season debut, with only a home run by Yoenis Cespedes leading off the second marring his night. Cespedes hit six of his 23 home runs and drove in 14 of his 83 RBIs in 19 games against Seattle last year as a rookie.
But after a one-out single in the third by Eric Sogard, Iwakuma retired the final 11 batters he faced before turning a four-run lead over to his bullpen.
Wedge said he would have sent Iwakuma out for another inning, but a blister on his right middle finger that hindered his last Spring Training start became a minor issue and he didn't want to push it.
"I felt fine from the get-go," Iwakuma said through translator Antony Suzuki. "But as we went along, it started to get a little tender. So 88 pitches was good enough for tonight."
The A's, who have hit .100 (6-for-60) in their first two games, were frustrated by this one.
"Obviously, last night was difficult for obvious reasons, with Felix coming out and pitching a game," said first baseman Brandon Moss, who went 0-for-3. "Tonight Iwakuma did well, but we squared some balls up. But we didn't make him pitch like we're capable of making him pitch.
"We almost had a passiveness to us, where we knew we weren't getting anything going, we were trying to make something happen instead of just playing loose," said Moss. "You feel things aren't there, and as a team you're not clicking and you're trying to make things happen, trying to force it. We'll come out tomorrow, and it can't be much worse than tonight."
The Mariners, on the flip side, will look to keep riding their early momentum.
"We're playing good baseball and it gets contagious," said Morse. "We're going to play with blinders on and just keep pushing forward."