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04/29/2013 11:11 PM ET

Stearns to fill in for third-base coach Datz

SEATTLE -- Minor League catching coordinator John Stearns joined the Mariners on Monday and replaced third-base coach Jeff Datz for the opener of a three-game series with the Orioles.

Datz was recently diagnosed with an undisclosed form of cancer and had some medical tests Monday that left him unavailable for Monday night's game. It's not known yet if he'll return for the final two games of the series.

Earlier Monday, manager Eric Wedge had indicated Datz was expected to work the rest of the homestand before sitting out the upcoming road trip to Toronto and Pittsburgh, but that changed shortly before the game.

Stearns, 61, previously served as a scout and, before that, as a Minor League manager with the Blue Jays, Reds, Mets and Nationals organizations.

When Datz revealed on Saturday that he had cancer, he said it was "very possible" he would miss some games, though he said in a statement he is not yet ready to publicly address the issue.

Datz, 53, has served as the Mariners' third-base coach for the past three seasons and has been a member of Wedge's coaching staff since 2003 with the Indians.

Back from DL, Saunders vows to keep all-out approach

SEATTLE -- Michael Saunders was activated off the disabled list and immediately installed by Mariners manager Eric Wedge as the center fielder and leadoff hitter for Monday night's series opener with the Orioles.

Saunders didn't miss a beat, swatting his second home run of the season in his first at-bat.

To make room on the 25-man roster, outfielder Carlos Peguero was optioned to Triple-A Tacoma.

Saunders has been on the disabled list since April 11 with a sprained right shoulder after crashing into the right-field wall at Safeco. In nine games this year, he's hit .286 with one home run and five RBIs.

Saunders' return is critical for a Mariners team that also has center fielder Franklin Gutierrez on the 15-day disabled list with a right hamstring strain.

In three rehab appearances with Tacoma over the weekend, Saunders went 2-for-11 (.182) with two runs, one double, one triple and two RBIs.

Saunders said he was able to cut loose with his shoulder and passed all the necessary tests to ensure he was ready.

"You get out there and your competitive nature takes over," he said. "You're not so tense. I learned in '08 [when coming back from shoulder surgery] that the last 5-10 percent is mental and just trusting that you're healthy and ready to do it. Once I was at the plate, I took hard swings and it felt good to let it go."

Saunders said he would play the same aggressive way he did before slamming into the wall tracking down a Jose Altuve line drive.

"There's no point in playing scared," he said. "I'm out there to play hard and that's the way I've always played. That was one of the tests, to make sure I felt like myself."

Peguero played in two games with the Mariners, batting .333 (2-for-6) with a home run and a stolen base.

Iwakuma's next start pushed back due to blister issue

SEATTLE -- Mariners right-hander Hisashi Iwakuma, who is fifth in the American League with a 1.67 ERA, will have two extra days of rest before his next scheduled start Sunday in Toronto.

Iwakuma has been bothered by a blister on the middle finger of his throwing hand since Spring Training, with manager Eric Wedge pulling him an inning earlier than normal in most of his starts. But he's still held opponents to a .160 batting average -- third in the AL -- while going 2-1 in six starts.

With an off-day on Thursday, Wedge has tentatively slated Iwakuma to throw the final game of the Blue Jays series as Joe Saunders leapfrogs him in the rotation to pitch Saturday. Felix Hernandez will throw Friday's opener.

Wedge said Iwakuma isn't completely finalized for Sunday just yet though.

"We're still working through that," he said. "A lot will depend on how we see the finger doing in the next couple days and how he feels when he throws his next bullpen."

Iwakuma threw six innings with just one unearned run in Sunday's 2-1 victory over the Angels and said his finger felt better than it had all season.

"That's the best he's come out of a game," Wedge said. "We didn't want to push him one more inning and have it get it back to where it has been, even with the extra time. He's working hard to get over the hump with this thing."

Pitchers swing away in advance of Interleague series

SEATTLE -- With a two-game Interleague road series upcoming in Pittsburgh next week, Mariners pitchers took a round of early batting practice on Monday and the results were mixed, as usual.

National League veteran Aaron Harang showed a strong bat and Blake Beavan also powered five balls over the wall while taking their hacks. Others weren't quite as smooth.

"I haven't hit since my sophomore year in high school," said 22-year-old rookie Brandon Maurer. "I wasn't too good then, I wasn't too good now."

But the session included much good-natured ribbing, fist pumps and smiles.

"It's a good time to get out there and just goof around and mess with each other a little bit and have some fun doing it," Beavan said. "We all used to hit for the most part in high school and stuff. Definitely not a comparison to this level, but we could all at least hit BP."

Beavan's last swing produced a drive above the Edgar's Cantina in left field.

"The last one was my best," Beavan said with a smile. "That was my goal, to put one in that upper deck."

Worth noting

• Mariners manager Eric Wedge said reliever Josh Kinney, on the 60-day disabled list with a stress reaction in his rib cage, is making progress while working at the training complex in Peoria, Ariz., and is getting closer to a rehab assignment. Kinney won't be eligible to rejoin the Mariners until May 30.

• Right-hander Erasmo Ramirez, who turns 23 on Thursday, is also in Arizona recuperating from a sore triceps muscle, but Wedge said he hadn't begun to throw yet.

Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB as well as his Mariners Musings blog. This story was not subject to the approval of Major League Baseball or its clubs.