KANSAS CITY -- Scot Shields was so efficient on Tuesday night -- six pitches, three outs -- he didn't even use a curveball that is behaving as well for him as it ever has in his seven Major League seasons.

"All fastballs tonight," Shields said on Tuesday.

The quality of his curve is one of the developments that have Shields feeling pretty good about things these days in his familiar role as setup man to closer Francisco Rodriguez.

Primary is the condition of his right arm, which caused him discomfort during a fitful spring in a couple of areas: shoulder, forearm. His big challenge coming into the season after a light spring workout load was to build and then maintain arm strength. That has happened fairly quickly, without a hitch.

"Everything feels good," Shields said, his ERA a club-best 1.84 with 12 strikeouts against only three walks in 14 2/3 innings over 14 appearances. "My breaking ball right now is the best it's been in a long time -- maybe ever. I'm getting on top of it, and I'm able to locate it right now."

Because of his arm angle, it's not a classic, over-the-top 12-to-6 curve. It's more like 2-to-8, giving it the appearance of a slider at times. He used to throw it at two speeds, but there wasn't a big difference, so he decided to stick with just one curveball this year.

How often he throws it, and how effectively, "depends on that day. Definitely I'm a lot more confident in it now."

His fastball, with uncommon sinking movement, remains his big weapon. Shields throws it about 70 percent of the time, he estimates.

Los Angeles manager Mike Scioscia credits the bullpen, how it has rounded into shape the past two or three weeks, as one of the main factors -- along with the superb starting pitching -- in the Angels forging to the lead of the American League West with twin aces John Lackey and Kelvim Escobar sidelined.

"Shieldsy has been lights-out," Scioscia said. "Sometimes hitters don't cooperate and swing when he has his good movement, and that brings up his pitch count.

"The ball's coming out of his hand really well. He's been making good pitches."

Coming into Wednesday night's series finale against the Royals, Shields hadn't given up a hit in his past four innings, allowing one walk. He hasn't yielded an earned run in 12 of his 14 appearances, holding hitters to a .235 average.

With Rodriguez back in form as well, leading the Major Leagues in saves with 14, the back end of Scioscia's bullpen once again is a force.