ANAHEIM -- Until further notice, lefty Brian Fuentes and righty Grant Balfour will reverse roles in the bullpen.

Fuentes will shift to setup duties, while Balfour will be the team's closer.

"I told Brian, that for now, until he has a few good outings in a row, that I would stick with Balfour," manager Bob Geren said before Tuesday's game in Anaheim.

The switch follows a rough stretch for Fuentes, who has been charged with the loss in each of his past four games. Owner of a 1-7 record and 5.06 ERA, the veteran southpaw is the first reliever to have seven losses before June 1 since Gene Garber also tallied that many in 1979 with Atlanta, according to the Elias Sports Bureau.

Balfour, meanwhile, had not allowed a run in 14 games -- spanning 14 1/3 innings -- until Sunday, when he offered up a game-tying home run to the Giants' Nate Schierholtz in San Francisco.

The gritty right-hander has not allowed a run in 19 of his 22 appearances this season and has surrendered just five total in 21 2/3 innings for a 2.08 ERA. He's tied for fourth among American League relievers in strikeouts (26) and has held opponents to a .192 batting average.

A's send down De Los Santos to make room

ANAHEIM -- When bringing up right-handed pitcher Guillermo Moscoso on Tuesday to start in place of the injured Tyson Ross, the A's went back to a seven-man bullpen and optioned reliever Fautino De Los Santos to Triple-A Sacramento.

De Los Santos spent just four days with the A's during his first big league stint and was never afforded the chance to make his debut, as the club relied on experienced arms during close games in that span.

Moscoso's start marks his first in the Majors, but the Venezuelan hurler boasts previous big league experience with the Rangers, having made 11 relief appearances spanning two seasons in Texas.

Acquired from the Rangers for another Minor League pitcher this offseason, the right-hander compiled a 3-2 record and 4.02 ERA in eight games -- seven of them starts -- for the River Cats before his promotion. He's expected to resume Ross' rotation spot until the righty is healthy.

Worth noting

• Right-hander Andrew Bailey, nearing a return from the disabled list, is scheduled to make his third Minor League rehab outing with Triple-A Sacramento on Wednesday. Bailey has yet to allow a run while with the River Cats.