BOSTON -- An 11-pitch at-bat against the Red Sox represented a hopeful shift in momentum for A’s All-Star Brent Rooker.

The 28-year-old Rooker, who was claimed off waivers from Kansas City on Nov. 22, wasted no time building his case for an All-Star election this season. Across 22 games in March and April, the outfielder hit .353 with a 1.245 OPS, nine homers and 22 RBIs. A stark difference from his numbers in May (.198 average) and June (.191 average).

Rooker hit his team-leading 15th home run in the sixth inning of Oakland’s 10-3 loss to the Red Sox on Saturday afternoon at Fenway Park.

“There have been times this year where I’ve been really productive and some times where I’ve struggled pretty heavily,” Rooker said. “And I think the way to succeed in this league, and at this level, is just learn how to balance those times out.

“Don’t get too high, don’t get too low, just kind of find some middle ground and stay there mentally, emotionally. I think that’s what gives you the best chance to have success.”

Rooker seemed poised to regain his early-season success in his first July game, breaking a 14-game homer drought with a two-run blast on the day his All-Star election was announced by manager Mark Kotsay.

But the power again disappeared, with Rooker going 2-for-16 from July 4 through the first four innings of Saturday’s game.

“The league makes adjustments on every young player,” Kotsay said. “When young guys come here and have success, the league’s going to do their homework. And I think they did, and I think it’s taken Rook a little while to make that adjustment back.

“But we’ve seen a good couple weeks from him, more consistent, and that’s a good sign.”

Veteran lefty James Paxton made Rooker work for his second homer in his past 20 games. Quickly falling behind, 0-2, after a called and a swinging strike, Rooker fouled off six pitches before sending a 2-2 cutter into the Monster seats.

“The deeper you get into at-bats like that the more comfortable you feel,” Rooker said. “Just because I’d fouled off fastballs, I’d taken breaking balls, I’d fouled off a changeup. So I had seen all the pitches and then kind of knew what tunnel I was looking for.

“And like I said. I was able to get the best one he threw me to hit there at the end.”

Red Sox center fielder Jarren Duran spoiled a two-homer day for Rooker, covering 94 feet to grab Rooker’s 101.8 mph flyout in front of Boston’s bullpen for the second out in the eighth inning.

“Rook took some good at-bats today,” Kotsay said. “The ball to right-center that he drove -- it was a great play by Duran. Duran’s pretty athletic out there, he’s showing what he’s capable of doing.”

Ahead of Friday’s series opener, Rooker had a visit from six-time All-Star and World Series champion Jonathan Papelbon.

Now a broadcaster with Boston’s regional network, NESN, Papelbon is a fellow alumni of Rooker’s alma-mater Mississippi State. The two had previously met when Papelbon visited the school while Rooker was still a student.

“He was just very congratulatory and animated as he is always,” Rooker said. “Been a few years since I’ve seen him, so it was good to see him. Just to get some words of encouragement from someone who’s had as much success as he has is always pretty cool.”

Outside of Rooker’s solo blast and JJ Bleday’s RBI single in the eighth, the A’s only other run of the game came courtesy of Manny Piña’s homer in the third inning, his first of 2023 after spending most of the first half on the injured list with a sprained right wrist.

“Manny’s grinded this year to come back from his injury, he hasn’t played in a while, I think it’s been close to 15 months that he’s actually been in a big league game,” Kotsay said.

“And it was good to see him in there, good to see him homer today.”