SEATTLE — As the A’s concluded the first half, one of their more surprising trends continued.

In the wake of Frankie Montas’ 80-game suspension for violating MLB’s drugs policy, Oakland’s rotation has stayed strong, with consistently solid performances throughout. On Sunday, it was No. 4 starter Daniel Mengden, who allowed three runs in the A’s 7-4 victory over the Mariners, the team’s seventh win in nine games.

Oakland’s win total going into this week’s All-Star break: 50.

“I just told them, ‘That’s pretty good,’ ” manager Bob Melvin said. “And I think, to a man, I don’t know if we’ve played our best baseball yet.”

Over the past 25 games, Oakland starters are 12-6 with a 3.87 ERA, and overall, the A’s pitching staff has a 3.29 ERA since June 11.

Less surprising: Matt Olson hammered his 19th homer in 51 games since returning from surgery to remove a broken hamate bone from his right hand. Olson has hit the most homers in baseball since May 12, and despite missing 36 games, he’s on pace to hit 46. He hit a three-run blast in the first Sunday.

“It feels like he’s got a homer every other day,” Melvin said. “He’s been absolutely fantastic.”

“Coming off the hamate, I heard a lot about power being lost, but pretty much when I started, I was able to fully swing,” Olson said. “The ball was carrying just as well. From that point, it’s just a product of better at-bats and better swings.”

His teammate, Matt Chapman, is Home Run Derby-bound, and Olson seems a great candidate for the event in coming years, but, he said, “I think it would definitely be cool. I’m honestly kind of bad at home run derbies. I don’t have necessarily the best batting practice. I don’t know how it would turn out. But I think Chappy will have a good run at it.”

The A’s also got homers from Marcus Semien and Ramón Laureano, solo shots, and the team’s 145 homers before the break established a franchise record, topping the previous mark of 137 set in 1996.

Oakland has homered in each of the past 12 games, with 24 in that span, and the team has hit 94 over the past 48 games. “It’s the strength of our team,” Melvin said. “We can hit home runs up and down the lineup.”

Mengden, who was recalled June 26 to take Montas’ spot in the rotation, left with a 6-2 lead and one on in the sixth, and reliever Ryan Buchter allowed Omar Narváez’s third RBI of the game, this one on a single.

Narváez also hit a solo homer in the second and an RBI single in the fourth. “I just didn’t throw him very good pitches today,” Mengden said. “I threw, I guess, very edible pitches for a hitter.”

Narváez added a solo homer in the eighth off Joakim Soria. Liam Hendriks earned the save before heading to the All-Star Game in Cleveland.

Mark Canha, who was out with back spasms Saturday, was in the lineup Sunday. He doubled and scored in the first inning. Chad Pinder had an RBI single.

The A’s trail Cleveland by 1 ½ games for the second wild-card spot, and they are 7 ½ games behind the Astros in the American League West.

Briefly: The A’s rotation out of the break was switched a bit because Brett Anderson is expecting the birth of his first child; Mike Fiers will start Friday against the White Sox, Chris Bassitt will go Saturday and Anderson on Sunday, just before Oakland’s day off. Mengden is likely to start the following Tuesday against Seattle and Tanner Anderson on Wednesday. ... Bassitt also is expecting the arrival of his first child at the end of August. ... The A’s will have a quick workout at 1 p.m. Friday after returning from the break.

Susan Slusser is a San Francisco Chronicle staff writer. Email: sslusser@sfchronicle.com Twitter: @susanslusser

Editor’s note: A previous version of the graphic with this story used A’s end-of-season records rather than records at the All-Star break from 2000 through 2018.

AL wild card Team W L GB* Tampa Bay 52 39 +½ Cleveland 50 38 — A’s 50 41 1½ Boston 49 41 2 Texas 48 42 3 * games behind 2nd wild-card team