OAKLAND, Calif. -- The fireworks show started early on Friday night at the O.co Coliseum, thanks to the Seattle Mariners.

Logan Morrison, Seth Smith, Nelson Cruz and Brad Miller each hit two-run homers in an offensive explosion that powered the Mariners to a 9-5 victory against the Oakland A's.

The Mariners haven't often lived up to their offensive potential this season, but this time they showed why so many expected them to go so far.

"You never know what's going to happen," Smith said. "We have guys 1 through 9 who are capable of doing really good things offensively, so you're not really surprised when they happen. It's not common for so many to happen in one game but you definitely take it when it happens."

One night after having just two hits in a 4-0 series-opening loss to Oakland, the Mariners had 13, seven for extra bases. Miller had a double to go with his homer. Second baseman Robinson Cano had three hits, including a double, and stole a base. Third baseman Kyle Seager had two hits, including a double.

The Mariners actually spotted Oakland and right-hander Jesse Chavez a 3-0 lead before scoring nine unanswered runs.

"I thought we did a really good job of battling," Miller said. "Early he got into a pretty good groove and things weren't going too well for us but we stayed with it. We were able to come up with some big hits and keep going because we know here in Oakland, every game we have with them is pretty tight, so you have to add on as much as you can for the last inning."

Seattle's home-run outburst -- two shy of its season high -- helped left-hander J.A. Happ (4-5) snap his four-game losing streak and win for the first time since May 9, also against the A's.

Happ gave up three runs on eight hits over six innings. He struck out five and walked none for the third time this season. He had nine straight starts without a victory, one shy of his career high, before Friday's win.

"It definitely seems like it's been a while, but for us to get a 'W' today was good," Happ said.

Chavez (4-8) gave up four runs and nine hits, including a season-high two home runs, over 6 1/3 innings. He struck out four and walked none. He had allowed five home runs all season until Friday.

Morrison hit a first-pitch, two-run homer off Chavez in the third inning, and Smith launched a 3-2 pitch over the fence in the sixth.

"You don't ever expect (them) to swing the first pitch, but a good hitter like that, guys go up there with a plan, he executed and I didn't," Chavez said of Morrison. "The other one shouldn't happen. Two outs. Get two quick outs and then you fall in a rut like that where you got an at-bat with Smitty who's a good contact hitter. Just made a good swing on the ball and got it out."

The Mariners trailed 3-2 entering the sixth inning, but Smith, who started in left field, put them ahead 4-3 with a two-run blast to deep right. With two outs, Seager drilled a single to center, and Smith crushed his seventh home run of the season.

Seattle added five runs in the eighth when designated hitter Cruz hit his 21st blast and Miller his eighth. Cruz lofted reliever Evan Scribner's 2-0 pitch over the right-center wall Cano on second after singling and stealing a base.

Later in the inning, Miller pulled Scribner's 0-1 pitch over the right-center wall with a man aboard to make it 9-3. It was the shortstop's eighth home run of the season.

"Recently the long ball's been his problem," A's manager Bob Melvin said.

NOTES: Oakland RHP Sonny Gray will miss his second straight start Sunday against Seattle but will avoid a trip to the disabled list as he continues his recovery from severe bacterial gastroenteritis, caused by salmonella. "We're not looking at Sunday but maybe shortly thereafter," A's manager Bob Melvin said. ... RHP Chris Bassitt, who started for Gray on Tuesday against Colorado is expected to start Sunday, although the A's have not made that decision official. ... After the game, Mariners manager Lloyd McClendon announced that right-hander Hisashi Iwakuma (right lat strain) will come off the disabled list Monday and start against Detroit. The Mariners also optioned LHP Roenis Elias, RHP Tom Wilhelmsen and LHP Vidal Nuno to Triple-A Tacoma. Corresponding moves will be announced Saturday. ... Mariners RHP Felix Hernandez will make his 38th career start and third this season against the A's on Saturday. He's 20-7 with a 2.63 ERA against Oakland.