SAN FRANCISCO — The Oakland A’s have lost their fair share of winnable games. Count their 6-5 walk-off loss on Saturday night in extra-innings to the San Francisco Giants among them.

The A’s entered the bottom of the 10th with a 5-4 lead gained on Matt Chapman’s sacrifice fly and left Oracle Park’s field as the home team mobbed Buster Posey’s back-up catcher Curt Casali for completing a two-run comeback against Oakland reliever Burch Smith.

Not as brutal, but equally as tense as a host of losses the A’s have lost in the margins of late. A flare and a home run separated win from loss on Friday against their Bay Bridge Rival. A series loss to the Yankees in New York came down to three total runs. The little things have the A’s three games back of the surging Houston Astros in the American League West. Even in the first half, the A’s are watching those standings.

“It sucks, definitely, losing that game,” Chapman said. “It’s been a fun two games considering the atmosphere. It’s nice playing in front of a lot of fans. I know how excited the Bay Area gets for this series. We’re definitely excited. We’re playing a team with the best record in baseball for a reason. They’re a lot like us, where they’re going to scratch and claw until the very end. They found a way to put two up on is in that inning.

“I felt really good going into that inning. I felt confident in Burch closing that inning. That’s baseball sometimes. Going down and losing the series like that definitely sucks. You want to get that win in front of the home fans.”

No one part of this A’s team is to blame entirely, but there’s always a finger to point after a gruesome loss.

Can’t point a finger at the starting pitching. Frankie Montas didn’t have his best stuff on Saturday, but held a potent Giants offense to two total runs on two hits. Those two runs came courtesy of LaMonte Wade Jr.’s two-run home run after the hitter went 0-2, fended off three foul balls and found a fastball he sent into the right field bleachers.

The Giants rang up Montas’ pitch count, and he left after five innings having walked three and struck out five.

Can’t point a finger at the defense. Saturday, the A’s defense saved at least two runs. Jed Lowrie extinguished a Giants threat in the sixth, robbing Steve Duggar of a possible RBI single with a leaping dive and get Yusmeiro Petit off the hook after issuing a hit and his first walk since May 15.

With the Giants threatening a walk-off in the bottom of the ninth, Tony Kemp and Chapman relayed Brandon Crawford’s near-walk-off single to get Wade by a few feet at home plate, sending the game to extra innings.

Point a finger at the offense, then. At times throughout this last week of marginal losses, the bats have failed to find the big hit that makes the difference. Saturday, though, Chapman had the big hit — his opposite field, two-run home run gave the A’s a 4-2 lead in the seventh inning. Against Giants starter Alex Wood, the A’s could only churn out a pair of runs. Elvis Andrus manufactured one on a single, error and wild pitch. Mitch Moreland, pinch hitting, hit a RBI single for their second run.

When the offense does its part against a tough pitching staff, frustrations can run high.

“What’s the frustration level? It’s frustrating,” manager Bob Melvin said. “After Chappy’s home run it felt like we were in a good spot to win the game. We had our best guys coming into the game. They came back and we ended up losing the game.”

Most tangibly, the loss fell on an A’s bullpen that’s struggled to hold leads of late. Smith hasn’t been his dominant 2020 self in 2021, accruing a 5.48 ERA. His 41.8% is up and his 19% strikeout rate is down. Maybe the runner-on-second rule in extras isn’t fair to any reliever, but he couldn’t hold Crawford, retire Duggar or Casali.

Sergio Romo returned to a familiar Oracle Park mound in the seventh and recorded two outs, but walked left-hander Wade.

Jake Diekman entered to face left-hander Mike Yastrzemski, but hit him with his first offering. Wilmer Flores knocked Romo’s runner in to make it 4-3. He left a pitch over the plate for Donovan Solano in the eighth inning, and Solano deposited it into the left field stands to tie the game 4-4.

Lou Trivino was particularly effective, striking out two in 1 2/3 scoreless innings, but an extra-inning bout calls for depth.

“Sometimes it’s not perfect. But what’s the alternative?” Melvin said. “Those are our best guys, and sometimes they’re going to give up some runs. You stick with them until you feel like you need to do something different…It’s easy to say switch things around, but you have to consider the alternative.”

The A’s bullpen as a collective has fallen in baseball’s ranks, ranking 22nd in MLB with a .6 WAR. They’re middle of the pack at 17th with a 70.4% left-on-base percentage and 4.04 ERA. No bullpen is perfect and late-game situations with wins and losses on the line can magnify the ebbs and flows of a reliever’s mistakes and triumphs. A Giants team with the best record in baseball got the best of them Saturday. But best believe the A’s are looking to bolster the bullpen before the trade deadline.

Melvin’s ejection: The A’s manager was ejected after a heated dispute with home plate umpire Lance Barrett after he called a borderline Diekman pitch a ball and appeared to get in catcher Sean Murphy’s face after it. Melvin gave Barrett an earful before and after his ejection.

“I didn’t like the strike zone,” Melvin said. “Thought it was a bad strike zone tonight. And then he showed up Murph, turned around and got in his face. So I didn’t like that.”