OAKLAND -- Those concerns about the quality of the A’s starting rotation, which have seemed legitimate through much of the season, could be on the verge of evaporating.

Mike Fiers sustained the starters’ recent surge with 5 2/3 effective innings, leading Oakland to a 8-3 triumph over the St. Louis Cardinals on Saturday night at Oakland Coliseum.

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Oakland’s fifth victory in six games wasn’t a particularly tidy affair. It required 3 hours, 35 minutes to complete. Half of the runners who scored for Oakland reached base on walks.

But Fiers remained above it all as he blanked the Cardinals for five innings.

“I’m always confident,” Fiers said. “I always go out there with the mindset to win that ballgame. I like to lead this team and put us in a great chance to win every time out.”

A’s manager Bob Melvin removed Fiers (10-3) after the All-Star right-hander surrendered a run and three hits in the sixth inning, Usually, Fiers might have remained in the game longer. But Melvin sensed that this represented an opportunity to provide a mild break for his ace, who threw 104 pitches or more in three of his previous six starts. Fiers totaled 94 this time.

Fiers’ stint was good enough to earn him his career-high eighth consecutive winning decision. His ERA dipped to 3.46, the product of pitching 18 consecutive games in which he lasted at least five innings and allowed three runs or fewer. That’s the longest such streak by an A’s pitcher since 1908.

“He’s been as good a pitcher as any in the American League for probably three months, to this point,” Melvin said.

This continued a welcome trend for the A’s. Their starters are 2-1 with a 2.65 ERA in the last six games after posting an 0-4 mark with an 8.69 ERA in six games preceding that stretch.The A’s will have further cause for optimism if right-hander Tanner Roark, their Trade Deadline acquisition from Cincinnati, can perform respectably in his Oakland debut on Sunday.

“I’m happy to be on a playoff-contending team, and I’m excited to do my part,” Roark said.

Oakland’s offense did its part against the Cardinals, who slipped a half-game behind the Cubs in the National League Central race. St. Louis starter Dakota Hudson (10-6) allowed four runs (three earned) in 3 2/3 innings and looked especially shaky at the outset as Mark Canha lined a two-run, first-inning single to open the scoring.

The Cardinals narrowed the difference to 5-2 in the seventh. A’s reliever Yusmeiro Petit did well to allow only one run to score after Jake Diekman left him a first-and-second, nobody-out mess to clean up.

Of the 44 baserunners that Petit has inherited this season, 13 have scored.

“He’s been doing it all year,” Melvin said. “It’s not the easiest role in the world, but he accepts it and he’s good at it. He’s not afraid of the moment, either.”

Chad Pinder’s second pinch-hit homer of the season, a three-run drive in the seventh inning off Cardinals reliever Tyler Webb, essentially settled the outcome. Pinder became the ninth Athletics player this season to reach double figures in homers, matching a franchise record reached in 2000 and 2017.