Josh Donaldson contributed with an opposite-field solo shot off reliever Lucas Luetge in the ninth, his third homer of the year just 12 games into the season. Last year, Oakland's third baseman didn't get his third until May 5.
Equally significant was Scott Kazmir's tremendous work, even though the lefty's day came to a halt after 82 pitches because of a minor bout of triceps tightness -- the same issue that kept him out of a Spring Training start last month.
Kazmir seemed rather confident, however, that he would not miss his next outing.
"I'm fine. Everything's fine," Kazmir said. "It's pretty much the same tightness that I felt in Spring Training. I don't know if it was dehydration or what, just felt like it tightened up as the game went on. Thought maybe I could power through it, but at that point it was just more about being cautious."
Oakland's veteran starter cruised through six scoreless innings but was then seen in the A's dugout holding his arm and talking with a team trainer and manager Bob Melvin, who sent lefty Fernando Abad out for the seventh.
"He wanted to go back out, but you want to be careful with a guy like that," Melvin said. "Up to that point, might've been his best start of the year. We've seen some good ones, but he was getting a lot of swing and misses, mixing all his pitches and was really good."
Kazmir really was brilliant, striking out nine and walking none. He offered up just two hits on the day, back-to-back singles to Brad Miller and Robinson Cano with one out in the fourth inning.
Through three starts this year, Kazmir has allowed only three earned runs and 11 hits with four walks and 19 strikeouts in 19 1/3 innings.
"He's giving us as good a chance as anybody to win," catcher John Jaso said. "He's putting us in the best possible position for that."
"Kazmir's been on fire," Mariners manager Lloyd McClendon said, "and he chewed us up pretty good today."
The victory is Oakland's sixth in its last seven tries, after the club started the year 2-3, and the team's starters have allowed three earned runs or fewer in every game this season.
A's pitchers posted a combined 2.00 ERA with 25 strikeouts in Seattle, and they combined for 17 consecutive scoreless innings against the Mariners to close out the series, with Sean Doolittle collecting the save on Sunday.
"We don't want to speak too much of it, just continue to go out there and keep doing it," Kazmir said of the starters' successes so far.
The A's stranded nine runners through the first seven innings, before pinch-hitter Jed Lowrie opened up the eighth with a walk and scored quickly on Cespedes' shot to left field off lefty Charlie Furbush, Cespedes' second homer of the year.
It came an inning after he dropped a fly ball in left field.
"My first swing, the second strike, I was trying to hit the ball too hard," Cespedes said through a translator, "and I took my head off of the ball. I told myself, let me make sure I'm comfortable with the pitch before I make the hard swing."
Mariners starter Chris Young had six scoreless innings, scattering four hits and three walks with two strikeouts. But all eyes were on Kazmir -- and will continue to be.
"That's the best I felt coming into the game," the lefty said. "It's just unfortunate it had to get cut short, but it's early in the year, so hopefully I get a couple more of those."