OAKLAND -- A challenging test awaits the Giants, as they’ll have to navigate the fourth-toughest schedule in the Majors down the stretch, according to FanGraphs.

After their next series against the Angels, the Giants will face five consecutive teams over .500 -- the Rangers, Rays, Braves, Phillies and Reds -- to close out their August slate, which looms as a potentially season-defining stretch for the club.

Given what’s ahead, the Giants missed a golden opportunity to bank some wins against the softer part of their schedule this weekend. San Francisco blew a three-run lead in an 8-6 loss to the lowly A’s on Sunday afternoon at the Coliseum, sealing a two-game sweep in the Oakland leg of the Bay Bridge Series.

While the crossbay rivals split the season series, 2-2, the A’s ended up reclaiming the Tom Pellack Memorial Bridge Trophy by virtue of their win in Sunday’s finale.

“Not a good baseball game,” manager Gabe Kapler said. “Not a good clean baseball game. We’re better than that as a group.”

The Giants’ slumping bats perked up against MLB’s worst pitching staff, scoring in each of the first three innings and knocking A’s starter Luis Medina out of the game in the fourth. San Francisco took a 6-3 lead into the bottom of the fifth, but the A’s began to claw back behind Nick Allen’s second homer of the game off All-Star right-hander Alex Cobb.

Cobb entered Sunday with the third-best ERA in the NL, but he wasn’t at his best against the A’s, allowing five runs (four earned) on seven hits over 5 1/3 innings. He was removed after surrendering a one-out double to Seth Brown in the sixth, though he exited the game after throwing only 77 pitches.

“I just didn’t have it,” Cobb said. “Not much life on the fastball or really any of the pitches. I was just kind of in battle mode all day.”

Kapler brought in right-hander Luke Jackson to relieve Cobb, but shortstop Brandon Crawford committed the first of two throwing errors on a grounder by Brent Rooker, putting runners on the corners for the A’s. Jackson then walked the next two batters before surrendering a two-run double to Shea Langeliers that put Oakland ahead, 7-6. The Giants had lefty Scott Alexander ready in the bullpen, but Kapler said he didn’t regret sticking with Jackson in that spot.

“Luke is an excellent, excellent reliever and has been for a really long time,” Kapler said. “He’s had a great year for us so far. I had no reason to do anything but trust Luke Jackson right there. I’ll keep doing it going forward.”

A forlorn Cobb watched the action unfold from the bench and rued his inability to deliver shutdown innings after the Giants’ offense put together one of its better performances in recent weeks.

“I just couldn’t believe that I had that opportunity in front of me today,” Cobb said. “The team seemingly gave me everything I needed early. I thought I made a good adjustment in the third. I was hoping to get on a little run there. I knew my pitch count was in a good place to be able to work deep. I thought I made the right adjustments, and I couldn’t string it together. I felt in that moment I had let the team down. I had a really good opportunity to flush what happened early. They gave me a new chance, and I wasn’t able to capitalize.”

At 61-51, the Giants are now tied with the Phillies for the top National League Wild Card spot and dropped four games out of first place in the NL West. While they’ve played well against contending teams, they know they’ll have to do a better job of taking care of business against weaker competition, as they’re now 34-27 against teams over .500 and 27-24 against teams under .500.

“To get where you want to be, you have to beat the teams you’re supposed to beat,” Cobb said. “It seems like this year we’ve been playing really good baseball against good teams. Letting two games go like that, hopefully it’s not going to cost us at the end of the year, but it definitely has the potential to.”