OAKLAND -- In anticipation of a packed house Saturday for the latest installment of the Bay Bridge Series, the A’s opened their parking lot gates earlier than usual for fans to get in their seats for first pitch.

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Once inside the Coliseum, the crowd of 40,065 -- largest of the season -- did not disappoint. Boisterous from the start, it was so loud at one point that A’s starter Adam Oller had to cover the PitchCom device on his ear with his hand in order to hear the signals from catcher Sean Murphy.

The Oakland faithful did its best to spur on the home team. But the A’s were unable to deliver, falling behind early in what ended in a 7-3 loss to the Giants in front of the largest crowd seen at the Coliseum since the sold-out audience for the 2019 American League Wild Card Game.

“Before the game, I was talking to [pitching coach Scott Emerson] and said this was the most people I’ve ever seen in this stadium,” Oller said. “I would have liked to perform a lot better in front of a crowd like that. But you definitely do notice that, especially in a big stadium like ours. It was loud. That was a really cool feeling.”

Oller, who is auditioning to stick in a rotation that now has an extra opening following the A’s trade of Frankie Montas to the Yankees on Monday, fell into trouble early. The right-hander walked three of his first six batters, yet managed to limit the damage in a 29-pitch first inning to just one run.

“That first inning with three walks, he was a bit shaky,” manager Mark Kotsay said of Oller. “Not sure if it was the excitement of the crowd or nerves going. Not his best command.”

Shaking off the first-inning scuffle, Oller managed to grind through five innings with the A’s facing only a one-run deficit. Though left-hander Kirby Snead was warming in the bottom of the fifth and Oller’s pitch count was up to 85, Kotsay -- perhaps in an effort to let the rookie build confidence -- allowed Oller to begin the sixth. But after Joey Bart led off with a single, Oller remained in the game to face left-handed-hitting LaMonte Wade Jr. and surrendered a two-run homer on a 1-2 fastball, spelling the end of his outing.

“You look at their pinch-hitters coming off their bench and the matchup that I had, I felt good,” Kotsay said. “Oller was working the ball well. I felt good that we could possibly roll Wade up and get out of it. It didn’t work out on our side. Overall, I think he still showed some progress today.”

Allowing four runs on eight hits and three walks over five-plus innings, Oller’s biggest frustration came from his inability to put hitters away. Despite consistently throwing first-pitch strikes, Oller said he did not have a good feel for his offspeed pitches. The result: Just one strikeout and only seven whiffs on 93 pitches.

“It was more nibbling in certain spots,” Oller said. “I did a good job of getting 0-2 and 1-2 on a lot of guys. I just didn’t have the putaway pitch. My breaking ball was all over the place, which makes things tough, especially in big situations where you need to put a guy away. I had a lot of opportunities to put guys away, and didn’t.”

While Oller may get another shot, the A’s are also likely to get a look at other arms over these final two months of the season in search of one or two starters who can become mainstays in the rotation. Another pitcher who will get that chance is A’s No. 23 prospect Adrián Martínez, who Kotsay confirmed will be recalled from Triple-A Las Vegas to start Sunday’s series finale against the Giants.

Other internal options who could get some starts with Oakland include left-handers Zach Logue (No. 21 prospect), JP Sears (No. 19) and Ken Waldichuk (No. 3). Spears and Waldichuk, who were acquired from the Yankees in the Montas trade, each made his organizational debut with Las Vegas this week.

With so many candidates for only a couple of spots, the A’s could explore the idea of a six-man rotation before the end of the season.

“We’ve talked a little bit about that possibility,” Kotsay said. “We do have some younger arms in our rotation that haven’t put in the amount of innings over the length of a season. Going to it right now isn’t in the cards. But we’re definitely discussing it and seeing how it may work in September.”