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8/8/2014 1:42 A.M. ET

Cook grows more comfortable with changeup

OAKLAND -- Ryan Cook returned from a right forearm injury in early June and, for about two weeks, was not his usual self. He allowed six runs in seven appearances and gave up two home runs, watching his ERA rise to 4.58. Since then, though, the right-hander has been untouchable.

Entering Thursday's series opener against the Twins, Cook had not surrendered a run since June 22, a span of 18 outings. He has 13 strikeouts and three walks during that stretch.

In addition to feeling fully healthy, Cook said Thursday that he has addressed a mechanical flaw that had been giving him trouble since last season.

"I was working at trying to find it, but it was just evading me," he said. "I was able to find that with the help of Curt Young, our pitching coach, and we made a couple changes there, which physically help you, and then also obviously help you mentally."

Primarily a fastball-slider pitcher, Cook has also become more comfortable this year throwing a changeup. Never one to shake off signs from his catchers, he has used the changeup sporadically during his career depending on who's behind the plate.

D-backs catcher Miguel Montero loved the pitch; former A's catcher Kurt Suzuki -- who is now with the Twins -- stuck with the fastball-slider combo; and now, Derek Norris, John Jaso and Stephen Vogt are bringing it back.

"In them calling it, I've learned a little bit on how to use it and when I want to use it," Cook said. "I don't shake [them off] much at all, actually, so it's more of a testament to them trusting in it and calling it at the right times than it is me deciding when to throw it."

Most importantly, Cook's command has been superb.

"It really is all about the command for him," manager Bob Melvin said. "When his arm slot's there, his mechanics are sound, you're going to see the results that you see. He was an All-Star at a young age for us [in 2012], and he's pitching as well as he's pitched here, including that year."

Lowrie still out of lineup, nursing swollen finger

OAKLAND -- A's shortstop Jed Lowrie was held out of the starting lineup for a third consecutive game Thursday because of a bruised right index finger. He pinch-hit in the seventh inning and lined out to right field.

Lowrie can easily swing a bat, but he still feels discomfort when throwing, and manager Bob Melvin would rather not use him at designated hitter during a stretch where he only has two other middle infielders with Nick Punto on the disabled list.

"If I DH, it kind of ties his hands, so I want to be able to throw and throw confidently," said Lowrie. "It's pretty swollen, it's pretty bruised. The way it hit me, I'm lucky it wasn't broken. It's just a matter of getting that inflammation out of there.

"If it's any other finger, it's not an issue, but because that's the finger that leaves the ball last, it's hard to control the ball throwing when you don't have good feel for the finger."

Melvin said he is "almost certain [Lowrie] will start" Friday.

"I think he could've played today, but at shortstop, if you get any number of throws that you have to make off-balance, he's still feeling it a little bit," he said.

Eric Sogard, who snapped a 110-game homerless streak Wednesday, made yet another start at shortstop in Lowrie's place Thursday.

Worth noting

• First baseman Kyle Blanks (left calf strain) is tentatively scheduled to go out on a rehab assignment with Triple-A Sacramento on Saturday and play in his first game with the River Cats on Sunday.

Jane Lee is a reporter for MLB.com. Aaron Leibowitz is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.