PHOENIX -- Zack Gelof's A’s legacy has barely begun being written, but on Sunday at Chase Field he secured a milestone that will forever go down in Oakland lore.

With a game-tying homer in the fifth inning of the A’s 5-1 loss in their series finale against the D-backs, Gelof recorded the 9,000th home run in Oakland franchise history.

The A’s are just the sixth team with at least 9,000 homers since 1968 -- their first season in Oakland -- joining the Yankees, Orioles, Red Sox, Tigers and Rangers in that span.

The swing put Gelof on an impressive list of A’s who have hit the milestone homers on the way to 9,000. In fact, it reads like a who’s who of Oakland baseball history, beginning with Hall of Famer Reggie Jackson, who hit the very first one on the list.

Oakland A’s milestone home runs
1 - Reggie Jackson, April 10, 1968
1,000 - Claudell Washington, May 6, 1975
2,000 - Rickey Henderson, June 5, 1983
3,000 - Dave Parker, Aug. 13, 1989
4,000 - Jason Giambi, May 17, 1996
5,000 - Jason Giambi, Sept. 24, 2000
6,000 - Bobby Crosby, May 31, 2006
7,000 - Brandon Moss, May 13, 2013
8,000 - Marcus Semien, Aug. 11, 2018
9,000 - Zack Gelof, June 30, 2024

One name on that list is of particular significance to Gelof, and that’s Crosby, the 2004 AL Rookie of the Year and current A’s first-base coach. Crosby was also Gelof’s manager at Double-A Midland in 2022, when the second baseman was climbing the club’s prospect rankings.

"From the get-go, he’s been a baseball player,” Crosby said. "He does everything right. He works the right way. He does the right things.”

Gelof moved on to Triple-A late that season and began 2023 there, before getting called up to the big leagues as the club’s No. 3 prospect on July 14. He had a breakout half-season with the A’s, with 14 home runs and 20 doubles in 69 games, but 2024 has been more of a struggle for the 24-year-old.

He hit .208 with five extra-base hits (three of them homers) in April and .153 with two extra-base hits (both doubles) in May. June, however -- while still below the pace he set as a rookie -- has started to see him come around. After going 1-for-4 on Sunday and 3-for-4 in the series opener, Gelof closed June hitting .247 with six homers for the month.

"He’s been working hard on making adjustments with the hitting coaches,” manager Mark Kotsay said. "The biggest thing that he’s learned is you have to continue to make adjustments, the league makes adjustments.

"You see another player on the other side, [D-backs reigning NL Rookie of the Year Corbin] Carroll, going through the same kind of year that Zack’s going through … but he’s starting to come out of it as well. And that shows the growth, it shows the commitment to making a change, which is tough. It’s tough to do in the big leagues."

Gelof has noticed the league adjusting to him and he’s embracing that challenge of making the counter adjustment.

"Last year I think I was getting a lot of four-seams up, and I feel like I’ve been getting less of those, more in-out, up-down type of thing, and mixing. So I just have to adjust back and focus on what I’m really good at and be as consistent as possible doing it."

This recent uptick in Gelof’s production comes as no surprise to his teammates.

"He’s a really good player,” DH Brent Rooker said. “He’s a special talent, and it’s fun to watch him play every day. And we know at the end of the year, the numbers are going to be there for him. He’s a good enough player where nobody in this locker room is worried about his production."

Unfortunately for the A’s, Gelof’s solo shot was all the offense they could muster against Brandon Pfaadt and the D-backs’ bullpen, spoiling one of the best starts of Luis Medina's young career. The right-hander went six innings, allowing one run on four hits with five strikeouts in a no-decision.

"Every game is different. You’re trying to make adjustments all the time,” Medina said. "Every game, you’re trying to get better. I just put myself into that, put everything into trying to do my best out there."

The D-backs got to T.J. McFarland and Austin Adams in a three-run seventh, sending the A’s on their way to the 17th loss in their last 21 games. They’ll look to regroup when they open a six-game homestand Tuesday against the Angels.

"We’ve been playing better at home than we have on the road,” Kotsay said. “We get a day off tomorrow again, which will be another day to get away and refocus and come back ready to play Tuesday."