SEATTLE (AP) -- Andrew Cashner cruised easily through five innings, only to see his outing derailed by one fluky call and one poor pitch.

That's just the way it's gone for the San Diego Padres over the past week, having lost seven of eight after a 9-3 loss to the Seattle Mariners on Monday.

The Padres' first interleague game of the season was going just fine until the sixth inning when the Mariners scored four times, capped by Kyle Seager's two-out, two-run homer on the first pitch from Cashner. Seattle then blew the game open scoring five times in the eighth off reliever Brandon Maurer, including a three-run homer from Dae-Ho Lee.

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"Outside of that I thought he threw the ball really, really well. There's not much to look at, he used both sides of the plate today, he varied his slider, mixed in his changeup. I thought he was great," San Diego manager Andy Green said of Cashner. "The sixth inning with the catcher's interference and just the pitch to Seager would be the only one in my mind that we'd have back."

Cashner pitched a season-high 6 1/3 innings and after keeping Seattle silent the first two times through the order the Mariners finally got to the right-hander in the sixth inning after San Diego had taken a 2-0 lead.

The rally started with Nori Aoki reaching on catcher's interference after clipping the glove of San Diego's Derek Norris. Aoki scored on Seth Smith's second double of the game and after Robinson Cano popped out for the second out of the inning, Nelson Cruz's ground ball found its way through the infield to draw Seattle even at 2-2.

The game was tied for just a matter of seconds. Seager jumped on the first pitch from Cashner driving it to deep right center.

"I just can't make a mistake with a changeup down the middle," Cashner said. "I thought I made some good pitches. They dug me out a couple times out of the zone, but overall I just can't make that changeup down the middle."

San Diego right fielder Matt Kemp had a chance to pull back the home run but hit the wall as he jumped and limited his extension. Seager's ball avoided Kemp's glove, hit off the top of the padded wall and bounced into the stands.

"Those things aren't taken back very often. When they do, they're unbelievably spectacular plays," Green said.

Seattle was able to hang around to rally in the late innings thanks to a solid outing from Nathan Karns (5-1), who won his fifth straight decision. Karns threw 6 2/3 innings, striking out six.

San Diego's Christian Bethancourt had an RBI single in the first inning and the Padres added another run in the sixth when Smith couldn't make a running basket catch on a fly ball by Brett Wallace and allowed Kemp to score.

"I thought one of the best games he's pitched for us all year," Seattle manager Scott Servais said. "Aggressive. Went after and finished hitters. He knew he needed to get deep in the game, we talked about it beforehand and he did and was efficient with his pitches."

UGLY EIGHTH

Seattle blew the game open in the eighth inning against Maurer. Adam Lind had a two-run single after Seager had been intentionally walked to load the bases. Lee followed with a three-run shot, his seventh home run of the season. Maurer allowed five earned runs after giving up four combined in his previous 15 appearances.

"People have bad outings sometimes," Green said. "It wasn't a crisp one for him at all."

TRAINERS ROOM

Padres: RHP Cesar Vargas will have an MRI on his right elbow when the team returns to San Diego. Vargas was placed on the 15-day DL on Sunday.

Mariners: SS Ketel Marte (thumb) is scheduled to join Triple-A Tacoma on a rehab assignment on Tuesday. If all goes to plan the Mariners expect to activate Marte on June 6 when the team returns from its trip.

UP NEXT

Padres: James Shields (2-6) starts for San Diego. He is 5-5 in his career against the Mariners.

Mariners: Hisashi Iwakuma (3-4) goes for his third straight victory. Iwakuma threw seven strong innings in his last start versus Oakland.