Who are the A’s eight best relievers?

The Oakland A’s bullpen didn’t blow a save this season until May 5, the team’s 32nd game of the year. They weren’t always perfect along the way, but for the first quarter of the season they bore down and got the job done when it counted.

They’ve finally hit their first notable slump over the past week or so. Four times in the last eight games, the relievers have coughed up a lead and earned a blown save in the box score.

• 5/15: Jake Diekman allows homer to Miguel Sano (A’s lose)
• 5/16: Jake Diekman allows homer to Andrelton Simmons (but A’s win)
• 5/21: Yusmeiro Petit allows triple to Juan Lagares (but A’s win)
• 5/23: Reymin Guduan allows sac fly to Shohei Ohtani (A’s lose)

Diekman was excellent last year, and he’s still been strong this year, and he’s 10-for-12 overall in save/holds. The same goes for Petit, who is still 7-for-8 and also leads the American League in wins. They were never going to be flawless for an entire season, so for now we can write off a brief hiccup.

The problem with that list is the final entry, in that Guduan was put into a save situation at all. And it was a particularly nasty one, with the bases loaded, one out, a one-run lead, and arguably the best hitter in the sport at the plate. The fact that it resulted in only a sac fly instead of a bases-clearing double was a matter of BABIP luck in Oakland’s favor.

That horrendous matchup was made possible by two things. One is questionable bullpen management, as the A’s used both of their co-closers in non-save situations earlier in the series — Lou Trivino pitched the 9th inning Friday with a four-run lead, and Diekman worked the 9th on Saturday with a four-run cushion, while Petit helped out both days. That overuse left Sunday’s options thinned, and the problem was exacerbated when that day’s starter went just five frames and they didn’t coax a second inning out of Burch Smith in relief.

But another factor is that Guduan is on the roster at all. He’s out of minor league options and can’t be sent down, and in April it makes sense to go out of your way to keep as many players in the organization as possible. But it’s late-May now, and it’s getting difficult to argue that Guduan is one of the eight best arms for the job.

• Guduan: 6.75 ERA, 13⅓ ip, 5 Ks, 5 BB, 1 HR, 19 hits, 4.50 FIP, .435 xwOBA

He doesn’t throw hard (94 mph), he’s not missing bats, and opponents are crushing him with a Statcast xwOBA that’s off-the-charts bad. Add in five wild pitches, and a blown save in his only opportunity. The nicest thing you can say about that stat line is that he’s left-handed.

It’s unclear whether the A’s see a hidden upside in the 29-year-old Guduan, or just want him as a replacement-level arm to eat innings during a marathon six-month season, and either answer is fine when the pitcher is just being used for low-leverage mop-up. But if the pen is going to run eight-deep and everybody is going to get turns in high-leverage, then there’s no room for luxury depth and there needs to be an emphasis on keeping the eight best arms in the pen.

So who are the eight best arms?

Most of them are obvious. Diekman, Trivino, Petit, Smith, and Sergio Romo are locks, even though Romo is having a bumpy early season. That’s five spots. Here’s the rest of the healthy 40-man roster:

• RHP Cam Bedrosian (in MLB)
• LHP Reymin Guduan (in MLB)
• RHP Deolis Guerra (in MLB)
• LHP Adam Kolarek (in AAA)
• RHP Miguel Romero (in AAA)
• RHP Jordan Weems (in AAA)

Also in Triple-A, but not on the 40-man, is RHP Domingo Acevedo, a high-profile minor league free agent who has struck out 13 of his 28 batters without a walk so far in seven innings for Las Vegas.

Are the using the best possible trio right now? Guerra has been perfectly decent in a long relief role, and even though he also got exposed Sunday in high-leverage he has at least been effective enough overall to keep around. Bedrosian just got called up and hasn’t pitched yet, but he’s got the best resume of anybody on the list and was good in a brief audition in Vegas. He’s earned a look.

That leaves Guduan vs. the rest of the list. Kolarek is a fellow lefty with an even uglier ERA, though most of the damage came against the Astros and he’s been fantastic against the rest of the league. Weems has already made a few appearances for Oakland, though he hasn’t been as sharp as we saw last year in his debut. Romero is one of the better prospects in the organization, but has been hammered so far this year in Vegas (5 ip, 8 runs, 3 K, 4 BB, 3 HR).

Perhaps none of this will matter much longer, as top prospect A.J. Puk has now made four rehab appearances for Vegas in his recovery from a strained biceps. If the plan is to put Puk in the pen after yet another injury, and if his return is indeed growing imminent, then that eighth spot could go to him any day now.

But some damage has already been done by getting too casual with the final bullpen slots, and trying to squeeze out too much fringe depth at the expense of actual wins. If manager Bob Melvin is going to use his closers in four-run games and ask everyone to take a turn in high-leverage, then he must be equipped with eight arms who bring maximum reliability, every day until Puk is back. Is that what he has at his disposal right now?

Vote in the poll below! Remember that if you pick anybody other than Guduan, then Guduan must be DFA’d because he’s out of options. And if you pick anybody other than Guduan or Kolarek, then the A’s will only have one lefty in the pen (Diekman). Acevedo would need a 40-man roster spot, but DFA’ing Guduan would clear one for him.