PHOENIX -- The Brian Fuentes experiment lasted less than half the time the Grant Balfour one did, and now neither are viewed as the A's lone closer.

Both are expected to still see ninth-inning action, though, as manager Bob Melvin has decided to move forward with a three-man closer-by-committee approach. Righty Ryan Cook, who has allowed just two runs all season, joins Fuentes and Balfour in the mix.

"I feel like we have three closers now," Melvin said Saturday. "We'll do the best we can to match up based on availability, left/right matchups. We'll do the best we can to get the guys in the right situations. I talked to all three of them."

The change comes less than 24 hours after Fuentes surrendered his second walk-off homer in as many weeks, the latest resulting in a 9-8 loss to the D-backs that was once a six-run Oakland lead. The left-handed Fuentes, who took over the ninth-inning role on May 13, has surrendered seven runs over his past four outings, forcing Melvin to stray from the one-man closer approach he prefers.

"I do," he said, referring to his preference, "but at this point in time, we're having a little bit of an issue with that. So, therefore, we're going to try a different group."

Cook has been lights out for the A's, evidenced by his 0.69 ERA spanning 26 innings. He ranks second among American League relievers in opponents' batting average (.085), and his .224 on-base percentage is sixth lowest. The numbers suggest the closer role may suit him best at the moment, but Melvin also acknowledged his value in other innings.

"I considered it, and it's very likely he could be the guy pitching in the ninth inning, but if there's one out in the eighth and the bases are loaded, he's probably my best option, too," he said of Cook, who appears to also be the A's most likely All-Star option. "You actually have to get to the ninth inning first.

"I'm open for anything right now. We're just going to try to get them in the best situations for them and for the team."

The right-handed Balfour, meanwhile, has showcased greater consistency his past few visits to the mound, turning in a 1.88 ERA over his last 14 games after allowing seven runs in 4 1/3 innings with two blown saves over his previous six contests.

Melvin earns third ejection at Chase Field

PHOENIX -- A's manager Bob Melvin was ejected by plate umpire Tim McClelland following the conclusion of the fifth inning in Saturday's 8-3 loss to the D-backs after taking issue with McClelland's strike zone.

"I was just arguing, yeah," Melvin said. "It doesn't really matter at this point."

It marked the third ejection of the season for Melvin, who was taking a stand for starter Jarrod Parker after a few questionable calls around the plate coincided with a five-run inning by the D-backs, who got a grand slam from Miguel Montero for a 6-1 lead.

A's bench coach Chip Hale took over managerial duties.

Worth noting

• Yoenis Cespedes (hamstring) took batting practice on Saturday, and how he fared during that session and during running drills was to determine his availability as a pinch-hit option.

• The A's claimed right-handed reliever Danny Farquhar off waivers from the Blue Jays on Saturday and optioned him to Triple-A Sacramento. To clear a spot on the 40-man roster, they transferred righty Andrew Carignan (elbow) to the 60-day disabled list.

Farquhar, who had a 2.97 ERA in 20 relief appearances for Double-A New Hampshire at the time of the move, began his career with Toronto but was traded to the A's with right-hander Trystan Magnuson for Rajai Davis in November 2010. He was then traded back to Toronto for left-handed pitcher David Purcey in April last year after appearing in four games for Sacramento.

• The A's on Saturday agreed to terms with four players from the 2012 First-Year Player Draft and have now signed 17 of their 43 picks.

Among those agreeing to terms was second-round selection Bruce Maxwell, a catcher out of Birmingham Southern. Joining him were right-handed pitcher Kris Hall (eighth round), outfielder Matthew Hillsinger (22nd round) and right-handed pitcher Ryan Dull (32nd round).