SEATTLE -- It was only the third inning, with a ton of baseball left to play. But a 13-pitch at-bat between Chris Flexen and Elvis Andrus proved to be the defining moment in the Mariners’ 6-0 loss to Oakland in a three-game rubber match on Wednesday at T-Mobile Park.

Flexen led off the frame with a walk to Matt Chapman after working the struggling third baseman into a 1-2 count. He seemed to reel it back in by inducing a flyout to the hot-hitting Tony Kemp. Then came Andrus, hitting .205 in the No. 9 hole, who proved to be far stingier than anticipated.

Andrus worked into a 1-2 count, saw one more ball to make it 2-2, then he fouled off seven of the next eight pitches and finally connected on a cutter low in the zone that didn’t have enough movement and caught a little too much plate, lining it into left field.

“It definitely snowballed after,” Flexen said. “He put up a great fight. I went right after him. He fouled everything off and he won the battle. He definitely changed the momentum there and I did a very poor job of executing after that.”

Chapman didn’t come around to score, but it was clear that lengthy sequence weighed on Seattle’s 24-year-old righty, who then gave up a two-run single up the middle to Mark Canha, an RBI single to Matt Olson and a 444-foot bomb off the batter’s eye to Mitch Moreland before escaping the inning, taking a five-spot back to the dugout.

Flexen needed 36 pitches in the third, and a short hook seemed inevitable. Yet he somehow managed to pitch his way through six innings, maintaining his efficient pace and lack of damage before and after that runaway third.

“There’s always room to be better,” Flexen said. “And I've done a very good job of limiting the big innings, the big numbers, and I definitely put us in a hole there.”

The Mariners’ bats offered just four hits (all singles), going quietly on a night when their cleanup hitter, Kyle Lewis, was seeking a second opinion on a torn meniscus in his right knee. A’s starter Sean Manaea was as good as he’s ever been in the big leagues outside his no-hitter in 2018, throwing eight shutout innings.

Though the optics of spinning a positive in a series-clinching loss are tough, Flexen did spell the bullpen by giving the Mariners length -- notable, given that they are almost certainly going to need a spot start on Friday in place of Justin Dunn, who hit the 10-day injured list earlier Wednesday with right shoulder inflammation. Flexen also allowed just three hits and zero runs in his other five innings.

“That's what you have to do as a Major League starter and certainly, we've been running our bullpen pretty hard here lately,” Mariners manager Scott Servais said. “You get the big inning early in the game like that, you've got to kind of wash it away, and I thought he did a pretty good job after that. He’s a little frustrated with himself. He wants to win the ballgame.”