SAN FRANCISCO -- Another nightmare inning from the bullpen doomed the Giants in a 15-3 blowout loss to the A’s in Sunday afternoon’s Bay Bridge Series finale at Oracle Park. 

The A’s erupted for nine runs in the fifth inning, crushing three homers off relievers Wandy Peralta and Dereck Rodríguez, to complete a three-game sweep of the Giants, who fell to 8-15 after losing 11 of their past 14 games.

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“I think the move is to very quickly address the issues, talk about what we can do better, continue to work on our process and then have a short memory and get ready for the next day,” manager Gabe Kapler said. “It’s the only way to do it in baseball when you play every single day. You don’t have a week to practice. You don’t even have a day or two days to get things straight. You have to talk about ways to build a better process. You have to turn the page very quickly and have a short memory.”

The A’s outclassed the Giants over the entire weekend, erasing five and three-run deficits in the ninth inning to stun San Francisco in the first two games of the series. Sunday’s finale, by contrast, was already decided by the time the ninth rolled around.

Looking to preserve their bullpen ahead of their upcoming home-and-home series against the Angels, the Giants sent catcher Tyler Heineman to the mound in the top of the ninth. Heineman hadn’t pitched in any formal capacity since college, but he delivered the most efficient outing of the day by a San Francisco reliever. Aided by a nice diving catch by center fielder Mauricio Dubón, Heineman faced the minimum and recorded a scoreless inning in his Major League pitching debut.

“I trusted that he would get on the mound and not try to do too much,” Kapler said. “The goal in those situations is to stay safe, lob the ball in there and see how quickly you can get them to put the bat on the ball and potentially hit into outs. I thought he did a really nice job for us.”

The same could not be said about the rest of the Giants’ bullpen, which entered Sunday with a 5.70 ERA, the sixth-highest mark in the Majors.

Rookie Logan Webb took the mound in the fifth with the game tied, 2-2, but he opened the inning by issuing his career-high fifth walk and was removed after retiring Marcus Semien on a flyout. Webb departed after throwing 88 pitches over 4 1/3 innings and was replaced by Peralta.

But Peralta misplaced a first-pitch fastball to Chad Pinder, who deposited it halfway up the left-field bleachers for a pinch-hit, two-run shot that put the A’s ahead, 4-2.

“I think that pitch to Pinder was just kind of a misfire in the middle of the plate,” Kapler said. “Pinder is a good hitter and was able to do damage on that pitch.”

The Giants wouldn’t recover. Matt Chapman and Matt Olson followed with back-to-back singles, setting up a two-run triple by Mark Canha. Robbie Grossman then drew a walk to chase Peralta, who faced five batters without recording an out.

Kapler subsequently brought in Rodríguez, but he, too, struggled to stop the bleeding, yielding a three-run homer to Stephen Piscotty and a two-run shot to Semien before finally ending the inning. The last time San Francisco allowed at least nine runs in an inning at home was May 5, 2016, against the Rockies, when they allowed 13 runs in the top of the fifth.

Giants relievers have surrendered 24 home runs through the first 23 games of the regular season, the most in the Majors. The club has allowed a home run in 19 consecutive games, the longest such streak in franchise history, according to Stats LLC.

“I just think we’re coming out and being aggressive with our pitches and some of them are missing in the middle of the plate,” Heineman said. “These guys are big league hitters, they know how to make adjustments and they’re putting good swings on the ball.”

The bullpen was one of the biggest question marks entering the 2020 season, and the Giants are still searching for answers with more than one-third of the campaign in the books. Left-hander Tony Watson is the only reliever with substantial back-end experience in the Majors, leaving Kapler with few trustworthy arms to work with. Tyler Rogers and Trevor Gott are viewed as high-leverage options, but they have both encountered stumbles this year. All three were unavailable on Sunday after pitching on back-to-back days, thinning Kapler’s selection even further.

The Giants have a handful of relievers who they hope will grow into bigger roles and potentially emerge as pieces for the future, including Caleb Baragar, Shaun Anderson and Sam Selman, but the group’s overall inexperience repeatedly cost the club over a painful series at Oracle Park this weekend.

“We knew that the early part of the season was going to be an exploration in learning about our relievers, particularly the ones that haven’t had much, if any, Major League experience,” Kapler said. “We knew that was going to come with some growing pains. That doesn’t take away the sting of not having success early in the season.”