PHOENIX -- Of the eight relievers who were on the D-backs' Opening Day roster, only one -- Joakim Soria -- is still in their bullpen.

So it shouldn't come as a surprise that Arizona's bullpen has had more than its fair share of struggles this year, the latest of which came Saturday night when San Francisco scored a pair of runs in the eighth inning to win, 6-5.

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Injuries have played a role in the changes to the bullpen, but so has ineffectiveness. The D-backs' bullpen ranks 28th in the Majors with a 5.23 ERA.

As a result, Arizona's front office has worked the waiver wire and free agency, leaving no stone unturned in order to try and find the right combination.

"First of all, our front office is never sitting still," D-backs manager Torey Lovullo said. "They're working day and night to better this particular team and better this organization. So it doesn't come as any surprise to me that we feel like we've made some necessary moves that, in our opinion, are considered upgrades. And that's just the nature of the game, where if you're not getting the job done, there's going to be some shifts. So yeah, the bullpen does have a totally different look."

On Saturday, the 'pen was needed in the fifth after starter Jake Faria allowed four runs in four innings. Joe Mantiply recorded two outs without allowing a run, Humberto Castellanos contributed 1 1/3 hitless innings and Noé Ramirez worked a scoreless frame.

Meanwhile, the D-backs' offense found a way to overcome an early 4-0 hole and took a 5-4 lead on a David Peralta RBI single in the fifth.

"Proud of the guys," said shortstop Nick Ahmed, who hit a game-tying two-run homer in the fourth. "I think we give up four there, and we came back and got two right away and then we keep fighting. You know, we go down, we fight, we come back, we take the lead. We just couldn't hold on. We'd like to have tacked on a couple more runs there, but we just didn't get it done."

The struggles of the bullpen have made it difficult for Lovullo to settle on any kind of roles.

"We've been walking through an assortment of guys, and they've had opportunities, some grasp it and don't completely clutch it and say it's theirs," Lovullo said. "And we're looking for that consistency. We've had some injuries, guys got a little banged up and we're missing a couple key pieces. But once again, that's an opportunity for somebody to step in and say, 'This is my situation, and I want it.'

"When you become that dependable, you're going to get that opportunity and you're going to anchor things, and we're looking for that. So it's been frustrating."

Lovullo turned to Ryan Buchter to pitch the eighth. The veteran left-hander, who had a non-roster invite to Spring Training and opened the season in the Minors, had been pitching well of late and had begun to earn more trust.

After recording two outs, Buchter walked Mike Yastrzemski. Then, he gave up a go-ahead two-run homer to Austin Slater that sailed way over the center-field wall, traveling a Statcast-projected 463 feet.

That proved to be the difference, and it sent Lovullo back to the drawing board.

"We can only do one thing -- keep handing the ball off to different portions of the bullpen and give them the opportunity to get the job done," Lovullo said.