SEATTLE -- Yusei Kikuchi put together his strongest performance in two months on Friday, but it wasn’t enough to stop the Mariners’ slide as Oakland pulled out a 5-2 victory in the series opener at T-Mobile Park.

Kikuchi’s progress is one of the major points of emphasis for a rebuilding Mariners squad this year and the 27-year-old rookie from Japan closed out his first half in positive fashion by allowing just four hits and three runs (two earned) over seven innings.

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“I’ve been in a bad stretch these last couple of starts,” Kikuchi said through interpreter Justin Novak. “The last two games I’ve been feeling pretty good, so I wanted to end the first half of the season on a good note.”

But two runs in the seventh -- one unearned after two errors on the same play by right fielder Domingo Santana -- proved costly for Kikuchi as the A’s overcame a 2-1 deficit. The loss dropped Kikuchi to 4-6 with a 4.94 ERA in 19 starts, including 1-5 with a 7.34 ERA over his last eight outings.

“Yusei threw the ball really well tonight,” said manager Scott Servais. “He had good stuff, as far as the velocity and break on his pitches. What was impressive to me, was I thought it was his best sequencing of his pitches that we’d seen really all year. He mixed in some really effective changeups. That’s becoming another real pitch for him, which is great to see, and he was very efficient in getting after them.”

Kikuchi has faced the A’s four times now and part of his learning curve has been adjusting to how teams are attacking him and changing his own approach.

“He's pitching a little bit differently now,” said A’s manager Bob Melvin. “Throwing more changeups, more sliders. He was mostly fastball-curveball when we first saw him. Even though we've had a couple games against him, he was an adjustment today based on the fact that he's pitching a little bit differently.”

Other than a solo home run by Franklin Barreto in the third, Kikuchi’s only trouble came when he gave up a leadoff double to Matt Olson in the seventh. Khris Davis then rolled a single to right that Santana couldn’t field cleanly, allowing Olson to score from second.

Santana then had a throwing error trying to get Olson at the plate, allowing Davis to move into second and eventually setting up the go-ahead run when Davis scored on a sacrifice fly by Ramon Laureano.

“Certainly the error in right field kind of messed up the inning,” Servais said. “It would have been first and third with nobody out, instead they got a run in and a man on second. That definitely affected the outcome of that inning.”

Kikuchi will head into the All-Star break awaiting the birth of his first child with his wife, Rumi, while having a chance to regroup and assess his season.

“I feel like I got off to a really good start and kind of hit a bumpy road,” he said. “There were a bunch of learning points during that time. Now I’m back where I want to be. I got to experience the ups and downs of a season in the first half and that’s going to help me grow in my career.”

Searching for offense

The Mariners have lost seven of their last eight games while scoring just 22 runs, dropping their record to 38-54 with two games remaining until the All-Star break. Oakland has won 13 of its last 17 to move into second in the American League West at 49-40.

Backup catcher Tom Murphy continued his strong season with a solo homer leading off the fifth to push Seattle into a 2-1 lead. The 28-year-old launched a 397-foot, opposite-field shot to right-center field for his ninth home run of the season in 35 games. He totaled 10 in 81 games over the previous four years with the Rockies.

The Mariners used the speed of Mallex Smith to pick up their first run as he led off the game with an infield single, stole second, took third on a throwing error and scored on a sacrifice fly by J.P. Crawford.

Smith ranks second in MLB in stolen bases with 23, while Crawford -- hitting in the No. 2 spot behind him -- has 15 RBIs in his past 13 games. But that was all the Mariners managed in a five-hit night.

“We have struggled offensively to put consistent rallies together,” Servais said. “We’ve hit a home run here or there or Mallex and J.P. create a run there in the first inning. But to put a string of four or five hits together or good at-bats, it has been a struggle. It’s why we’re not scoring runs. You’ve got to group them together.”