OAKLAND -- Seth Brown has always been viewed as a player who projects to put up some serious power numbers when given a full slate of playing time. After an early-season scuffle at the plate, that potential is now starting to show through.

Crushing a two-run homer as part of a two-hit effort in the A’s 6-4 loss to the Giants on Sunday, Brown continues to perform as one of baseball’s most prolific sluggers in the second half. Since the A’s returned from the All-Star break, Brown’s seven home runs are second-most in the Majors behind only Yankees star Aaron Judge, who has 10 over that span.

Brown’s power surge has keyed an improving A’s offense that entered Sunday with 32 home runs over its past 21 games dating back to July 11, which ranked second among American League teams.

“He’s been really turning it on,” said A’s catcher Sean Murphy. “He’s just pounding homers for us. Extra bases. Driving guys in. That’s what you want out of the guy hitting in the four-hole, and he did it again today.”

Brown has experienced his share of ups and downs going through his first full season in the big leagues while facing high expectations as the essential replacement of former A’s All-Star first baseman Matt Olson. Once his batting average dipped severely below the Mendonza line in mid-May, Brown adjusted his approach to focus on attacking the left side of the field.

Brown’s offensive numbers have been on an upward trend ever since. In 12 games back from the All-Star break, Brown is now 16-for-40 (.400) with 10 RBIs, nine extra-base hits and a slugging percentage just under 1.000.

With Sunday’s homer off Dominic Leone, his 17th of the season, Brown remains on pace to significantly surpass his career highs in several offensive categories.

“Real happy with Seth,” said A’s manager Mark Kotsay. “I talked about it when I recognized the change in approach. He was starting to take the baseball the other way. A while back, I talked to him about if he continued to stay with that approach that, at the end of the year, he’d look up and be pretty satisfied with his numbers.

“He’s in line right now and moving in that direction. We’ve just got to keep him there and focused on that approach. He’s done a great job with laying off some offspeed down in the zone that he was swinging and chasing at earlier in the year.”

Brown’s offensive contributions weren’t enough for the A’s to avoid a two-game sweep at the hands of their cross-bay rivals. However, a positive taken away from Sunday was the performance by rookie starter Adrián Martínez, who struck out five batters and limited San Francisco to two runs on four hits and a walk over 4 1/3 innings.

Making his fifth career Major League start, Martínez, Oakland’s No. 23 prospect, returned from his previous demotion to Triple-A Las Vegas last month showing the exact improvements the A’s wanted to see him make upon his departure.

Working off better command of his fastball, Martínez managed to generate a career-high 14 whiffs (swing and misses) on just 69 pitches, marking the lowest pitch total of his five starts with Oakland. His best weapon was his changeup, which registered eight of those whiffs as he threw it 24 times.

“I thought Martínez did a good job,” Kotsay said. “Outside of that 0-2 mistake to [Mike] Yastrzemski, for me, he looked like a different pitcher today. We’re continually working with Adrián on his mechanics to get him down the line. He’s made improvements. Just watching today, the slider had more depth. It wasn’t side-to-side. The fastball had life with some sink. I think he’s moving in the right direction right now.”

With an opening in the starting rotation following the departure of Frankie Montas, Martínez is one of a handful of candidates the A’s are evaluating as they search for a more permanent fixture in that No. 5 spot. Having been disappointed with his previous start in the Majors prior to the All-Star break that led to him getting sent down, Martínez said he was able to pitch more to his strengths this time around.

“This was a much better outing,” Martínez said. “I was working on my command and throwing a lot of changeups. I felt good physically and mentally. I was attacking the zone and stayed aggressive on every pitch. I’m just going to keep working and try to take advantage of this chance to stay here.”