SEATTLE -- Somehow, Paul Blackburn was more nervous about his second major league start than his first.

"I had a lot more anxiety before going out to pitch," Blackburn said. "I took a lot of deep breaths."

That seemed to work. The Oakland right-hander scattered eight hits in 7 2/3 innings for his first major league victory as the Athletics defeated the Seattle Mariners 7-4 Thursday night at Safeco Field.

The rookie, who was acquired from Seattle in an offseason trade for first baseman Danny Valencia, walked one and didn't strike out a batter. The only run he allowed came on a solo homer by Mitch Haniger.

"Your first start is kind of an out-of-body experience, and then your second start is about performance," A's manager Bob Melvin said. "He throws the ball where he wants to and mixes his pitches. There's something to be said for that. It's not always about velocity. It was a really, really good performance from him."

The Athletics (38-48) earned their third consecutive win after snapping a season-high, six-game losing streak.

Valencia hit a three-run homer, his ninth of the season, off A's reliever Daniel Coulombe with one out in the bottom of the ninth for the final margin.

Seattle (41-46) took its eighth straight home defeat.

"Not much to say about that ballgame," Mariners manager Scott Servais said. "We've got to figure it out."

Blackburn, who gave up only one unearned run on three hits in his debut Saturday against the Atlanta Braves but didn't get a decision, retired the side in order only once Thursday.

He allowed hits in the first three innings but got double plays in each.

"I'll definitely take a double play over a strikeout every inning," Blackburn said.

The Mariners put two runners on in the fifth before Blackburn induced cleanup hitter Nelson Cruz to ground into a fielder's choice to end the inning.

"Everything was working for him," A's catcher Bruce Maxwell said of Blackburn. "He's a bulldog on the mound. He made pitches the whole night. That's his game. He doesn't throw 98 (mph), but he keeps hitters off balance.

"His first big league win, and I'm glad I got to catch it."

Blackburn (1-0) was replaced after allowing a two-out double to Segura in the eighth. Left-hander Coulombe came on to induce an inning-ending groundout from Ben Gamel, who entered the game as the American League's leading hitter.

The A's struck early against Seattle starter Sam Gaviglio (3-4), scoring three runs in the first inning.

Matt Joyce led off with a single, Marcus Semien walked, and Yonder Alonso, Oakland's All-Star representative, hit a run-scoring double down the right field line. An out later, Jed Lowrie smacked a two-run double to right-center field.

It was Semien's first game since April 15, when he sustained a fractured scaphoid bone.

"We talked about this when Marcus was coming back, and guys were really excited about it," Melvin said. "Just ... looking at the lineup now, you know, it gets pretty deep. And there just seemed like there was good symmetry to it. And to get off to a good start where we score three runs right away ... guys were all talking about it in the dugout.

"It was an exciting inning for getting Marcus back and moving some guys around a little bit and getting some production."

Oakland extended the lead to 7-0 in the fifth.

Semien led off with a single and stole second. Following a walk to Alonso, Khris Davis hit his 24th home run of the season, a three-run shot to right field.

Lowrie singled but was erased on a double play, and then Bruce Maxwell hit his first homer, a solo shot.

It was easily the worst of Gaviglio's nine career starts. The rookie right-hander lasted just 4 2/3 innings, the first time he failed to make it through the fifth. He gave up seven runs on nine hits, including the two home runs. He walked three and struck out six, which matched his career high.

The Mariners snapped the shutout on Haniger's homer with two outs in the bottom of the fifth.

"Sam Gaviglio was not sharp," Servais said, "and offensively we didn't get much going at all."

NOTES: Bob Melvin earned his 500th win as Oakland's manager. He is 500-495 with the A's, 993-1,003 overall in 14 seasons as skipper of the Mariners, Arizona Diamondbacks and Oakland. ... Seattle SS Jean Segura went 4-for-4 with a double, his fourth four-hit game of the season. ... Mariners RHP Yovani Gallardo pitched 4 1/3 scoreless innings of relief. ... Seattle 3B Kyle Seager snapped an 0-for-14 drought with a single in the second inning. ... The A's placed RHP Jharel Cotton (right thumb blister) on the 10-day disabled list, clearing a roster spot for the return of SS Marcus Semien. ... Oakland LHP Sean Manaea (7-4, 3.75 ERA) is scheduled to face Seattle LHP James Paxton (6-3, 3.27) on Friday.