SEATTLE — Edwin Diaz couldn’t hold the line.

Diaz entered a tie game in the ninth inning on Saturday, but he gave up a leadoff single that turned into the decisive run in the Seattle Mariners’ 4-3 loss to the Oakland A’s.

After three straight appearances in which he’d given up a combined seven runs (three earned) at the end of June, Diaz hadn’t allowed a run in in his last two outings; he’d also only allowed one hit in those two outings.

But Diaz gave up an infield single to A’s outfielder Rajai Davis to start the ninth inning. He then got a strikeout as Davis stole second. The Mariners intentionally walked Yonder Alonso, who had homered earlier in the game, to face Ryon Healy.

But Healy drilled a ground-rule double into the right-center gap, allowing Davis to score the go-ahead run.

Mitch Haniger gave the Mariners life in the bottom of the ninth. He crushed a two-out double to center that tipped off the glove of Davis. But Jarrod Dyson flied out to left field to end the game.

It spoiled another quality start from rookie starter Andrew Moore.

In his third career start, Moore gave up three runs in six innings, his shortest start to date, but he did exactly what the Mariners want: He kept them in the game, and he didn’t tax the bullpen.

Moore did, however, do something for the first time in his career.

He had gone 69 batters without walking anyone to start his MLB career, the longest such streak to start a career in team history. He then walked two batters, back to back, in the fourth inning. He also hit a batter in the fifth.

Moore gave up two more home runs — that’s five in his three starts — but both were solo shots.

Moore’s fastball is usually in the low 90s, and he is neither overpowering nor dominant with the quality of his pitches. But Mariners manager Scott Servais said Moore has other assets.

“I think his ability to throw strikes to all different quadrants in the strike zone is really valuable,” Servais said. “Probably does it as good as any young pitcher I’ve seen in a while. Does he have the overpowering strikeout pitch that everybody goes, ‘Wow’? No, he doesn’t. Not the nasty curveball or slider. But you put all of his pitches together, and they all work very well together, and they all play above average for him. But if you put each one of them in a vacuum, they’re probably average, maybe a tick below. But the sum of the parts are greater than the parts themselves.”

The Mariners picked up Moore whenever he stumbled Saturday.

After Moore put the Mariners in a 2-0 hole in the top of the third inning, Jarrod Dyson doubled, then scored when Jean Segura also doubled. Segura scored to tie the game on a single from Ben Gamel.

When Moore gave up a home run in the fifth inning to give the A’s a 3-2 lead, Dyson tied the game with a solo home run, his fifth this season.

All of those runs came off A’s starter Chris Smith, who has a remarkable story. Smith is 36, and was making his major-league debut after so many years in the minors.