Moscoso is expected to join the club's 25-man roster on Tuesday, when the A's are likely to option a member of their eight-man bullpen to make room for him. The 27-year-old Venezuelan, who is already on the team's 40-man roster, boasts big league experience, having made 11 appearances -- none of them starts -- with the Rangers, including 10 in 2009 and one last season.
Acquired from Texas for another Minor League pitcher this offseason, the righty has compiled a 3-2 record and 4.02 ERA in eight games -- seven starts -- for Triple-A Sacramento.
"He's been pretty consistent," A's manager Bob Geren said. "He's throwing strikes, and he's ready to go. He has a good breaking ball, and when he throws it at the right speed, it's pretty good. He throws a changeup any time and has pretty good command of his fastball. He's off to a decent start."
Moscoso will take the rotation spot of Tyson Ross, who suffered a left oblique strain just seven pitches into his start on Thursday.
For the Angels, it's the same old story for hard-luck Haren, who has gone six starts without a win. He was 4-0 in his first five appearances and is 0-2 since then despite allowing only 11 earned runs in 42 1/3 innings (2.34 ERA), walking 10 and allowing 32 hits while striking out 39.
"The story of my life," Haren recently said. "I'm sleeping well."
Angels manager Mike Scioscia was a bit more descriptive when asked about the situation.
"Danny, he's been through this before and understands there's only so much you can control," Scioscia said. "He understands guys on the offensive side are trying, but he just hasn't had any luck. We haven't seen everybody [on the mound], but there aren't many guys who have been as consistent as Dan start to start.
"Hopefully, we'll start to support him and his win-loss record will support the way he's pitched."
A's: Geren downplays importance of series
Geren said he didn't want to make too much of a big deal of who the A's are playing in this series -- just how they're playing. "It's just we've been in a little bit of a skid. Five days ago, we're at the top of the world in first place with a big blowout win, and we've hit a pretty good road bump. It's time to get going, because it's a long season."
Moscoso faced the Angels as a reliever at Angel Stadium in 2009, going 2 1/3 scoreless innings, allowing striking out two and walking one.
Reliever Craig Breslow has not allowed a run in 16 of his last 18 outings (four earned runs in 16 innings for a 2.25 ERA) and has stranded all seven of his inherited runners over that span.
Angels: Bullpen back on point
Angels relievers have allowed just one earned run in their last 12 1/3 innings pitched after surrendering 15 earned runs over their previous 16 innings. Setup man Scott Downs has pitched scoreless ball in 14 of 15 outings, and the Angels are 10-5 in games in which he has appeared.
Infielder/outfielder Howard Kendrick's bat is still missing in heart of the order as he recovers from a right hamstring strain. He has missed four games, including Monday.
The Angels have 11 one-run losses this season. They lead all of Major League Baseball in that category.
A's outfielder David DeJesus has not committed an error in 39 games in the outfield and has a 280-game errorless streak, which is the longest active streak among all Major League outfielders. He last committed an error Sept. 15, 2008, against Seattle in center field. ... The Angels have hit 10 home runs in 23 home games compared to 28 home runs in 26 road games.