On a Mariners team filled with rookies and young players, Kyle Seager stands out. And not just because he’s the only veteran position player getting regular playing time on a rebuilding club that finished off a doubleheader sweep of the A’s on Saturday with a 12-3 blowout in Game 2.

Seager homered in both games of the twin bill to reach 500 extra-base hits in his career, joining Edgar Martinez (838), Ken Griffey Jr. (788) and Jay Buhner (557) in that exclusive group in Mariners’ history.

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The 32-year-old leads the Mariners with 40 RBIs, ranks second to rookie sensation Kyle Lewis in home runs, with nine, and he has almost the exact same on-base and slugging percentages as Lewis, at .361 and .442 (with Lewis at .366 and .443).

So while Lewis has received rave reviews as the expected American League Rookie of the Year Award winner, Seager quietly has continued producing and setting an example for his youthful peers.

“Kyle has been huge,” Mariners manager Scott Servais said. “Certainly on the field, he’s been very productive and probably having one of the most consistent seasons he’s had. But behind the scenes, showing up, going through our early work every day. He hasn’t missed a day.

“He will play in all 60 games this year, and I don’t know how many guys in the league have done that, but it’s something he takes a lot of pride in, being able to play every day. And I certainly appreciate it as the manager. He’s meant a lot to our club, and it’s nice to see him getting rewarded here at the end. He’s really swinging the bat well.”

Seager has checked off several milestones this year, surpassing 200 career home runs and 700 RBIs. Now he’s added the 500 extra-base hits.

“It’s a big number and something I’m extremely proud of,” Seager said.

He’s also proud of the progress his young club has achieved. While the Mariners have been eliminated from postseason contention, they’ve gone 19-13 since Aug. 21 and provided a strong sense of better things ahead.

“We’ve definitely made some strides,” Seager said. “You’ve got some pieces that you can see moving forward. Guys played hard. The effort was there. We stole a lot of bases. We played pretty good defense. There are definitely things to like. Our pitching was solid, we had some starters step up and establish themselves, and I thought our infield defense, J.P. [Crawford] was phenomenal. He took a big step forward. I thought he was tremendous this year.”

Seager became just the sixth Mariner ever to homer in both games of a doubleheader, joining José Marmolejos (earlier this year), Alex Rodriguez (2000), Martinez (‘99), David Segui (‘98) and Buhner (‘90).

“The doubleheaders are a different animal this year,” Seager said of the seven-inning contests. “To be able to do a little damage, it makes the day a lot more fun. Winning makes the day a lot more fun, too. When you’re winning and hitting homers, everybody is pretty happy.”

With the A’s starting right-hander Paul Blackburn, who was called up from their alternate training site as the 29th man for the doubleheader, the Mariners scored eight times in the third inning and wound up with their highest run total of the season.

Rookie first baseman Evan White went 3-for-4 with two RBIs on a double and home run and Tim Lopes slugged his second long ball of the year. White’s 440-foot homer was the second-longest recorded by a Mariner this season, per Statcast, behind only a 446-footer by Ty France.

Starting pitcher Justin Dunn didn’t have his best stuff, but he went five innings and gave up three runs on six hits -- including a pair of solo homers by Robbie Grossman -- to finish his rookie season at 4-1 with a 4.34 ERA. The 25-year-old right-hander went 3-0 with a 2.10 ERA (6 ER, 25 2/3 IP) in his final six starts.

Oakland has already clinched the American League West title and takes a 35-24 record into Sunday’s season finale. The Mariners are 27-32.