SEATTLE -- An outstanding start by Yusei Kikuchi went by the wayside for the Mariners on Saturday, as Oakland rallied under MLB’s new extra-innings rules to pull out a 3-2 victory in 10 innings.

The loss snapped Seattle’s three-game win streak and kept the young Mariners from moving into first place in the early American League West race, as they instead sit a half-game back of the A’s and Astros with a 4-5 record.

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Kikuchi held a 2-0 lead after throwing six scoreless innings, but the A’s tied the game at 2-2 with a two-run homer by Chad Pinder in the seventh off reliever Nick Margevicius and then pushed across the go-ahead run in the top of the 10th with an RBI double by pinch-hitter Robbie Grossman, scoring Tony Kemp, who started the inning on second base under the new MLB extra-innings rule for 2020.

The Mariners missed a chance to win it in the bottom of the ninth after loading the bases with one out, and they couldn’t capitalize with the runner starting on second in the 10th either, as Tim Lopes popped out on a bunt attempt, Dylan Moore flew out to shallow left field and J.P. Crawford struck out.

“The 10th-inning rule, our first go-round, it’s such a different feel to it,” Mariners manager Scott Servais said. “It doesn’t matter if we’re a fan of it or not, it’s the way the game is played right now. You have to get big hits and execute, and we just weren’t able to do it late in the game today.”

But the pain of a frustrating loss was at least countered by the bigger-picture progress of Kikuchi, who could be a long-term mainstay in the rotation if he pitches like he did in his second outing of the season.

Kikuchi struggled through much of his rookie season in 2019 and gave up five runs in 3 2/3 innings in Houston in his 2020 debut, but he bounced back strongly against the A’s while looking much more like the starter the Mariners were hoping for when they signed him as a free agent out of Japan on Jan. 2, 2019.

Servais called it Kikuchi’s best outing other than a late-season shutout in Toronto last Aug. 18. He said it was great to see the 29-year-old lefty pitching with confidence, with his slider and curveball combo helping complement a fastball that averaged 95.2 mph on Saturday, which represented Kikcuhi's second-fastest average four-seam fastball velocity in any start to only his 2020 debut last Sunday.

“Conviction is the right word,” Servais said. “He should believe in his stuff. It’s really good. It’s as good as left-handed stuff as you’ll see in the league right now. It’s that overpowering. I’m looking forward to seeing him pitch the rest of the year because he’s going to have a lot of good outings if he keeps doing that.”

Servais felt that Seattle's rotation was an underrated element of his club coming into the season, but that was a tough argument to make after the six starters combined for a 10.55 ERA their first time through.

Yet that script has flipped since then, and Kikuchi continued the turnaround, as he allowed just three hits and one walk while striking out nine -- one shy of a career high -- in a dominant performance.

In the past three games, Mariners starters Marco Gonzales, Taijuan Walker and Kikuchi have allowed just two unearned runs, with 23 strikeouts and four walks in 19 1/3 innings, a far cry from the combined 28 runs (24 earned) in 21 1/3 frames in the initial go-round.

Kikuchi said that he took his cue from watching Gonzales and Walker before him.

“In Houston, I fell behind in the count a lot and put myself in tough situations,” Kikuchi said through translator Kevin Ando. “This whole week, I was working in the bullpen on being aggressive in the zone with my stuff. Watching Taijuan and Marco go out there and just pound the zone really made me realize the importance of being aggressive.”

With the starters still building their arm strength after the short Summer Camp prep time, Servais pulled Kikuchi after 89 pitches. But the lefty said he’s feeling strong and was pleased to be able to hike the velocity on his slider up to the 92 mph range, which is something he’s worked on since last season.

“Gaining velocity on not only my slider, but my fastball as well, was one of my main goals this offseason,” he said. “Last year it was a little slower and I wasn’t getting as many swings and misses as I wanted. So I’m really happy to see that velocity.”

Kikuchi allowed just an infield single in the first five frames before yielding a pair of leadoff singles in the sixth. But he struck out Sean Murphy on a 93 mph slider and Marcus Semien on a 96 mph fastball before ending his outing with a groundout from Matt Chapman.

“His competitiveness really stood out tonight,” Servais said. “This was a huge learning experience for Yusei in getting over the hump. Getting out of that sixth was outstanding for him in a big outing.”