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4/9/2014 10:12 P.M. ET

Iwakuma pleased with first throwing session

SEATTLE -- Injured right-hander Hisashi Iwakuma threw 34 pitches in his first bullpen session of the year Wednesday at Safeco Field, another step toward a potential return later this month or in early May.

The 2013 American League All-Star sprained the tendon on the middle finger of his throwing hand just prior to Spring Training and was unable to grip a baseball until late March. He had been playing long toss in the outfield over the past week before finally getting on the mound Wednesday.

Iwakuma said all went well as he threw mostly fastballs with a few curveballs mixed in. He'll add some sliders for his next bullpen session, which is scheduled for Saturday, his 33rd birthday.

The goal is to build up his arm strength and pitch count and then begin a Minor League rehab stint, most likely with Triple-A Tacoma. There is no target date yet there, as everything hinges on Iwakuma feeling strong and progressing without any setbacks to his finger or arm.

"We'll take it one day at a time," Iwakuma said through interpreter Antony Suzuki. "We'll leave it to the trainers and pitching coach as to what they see, and hopefully, from my standpoint, soon. But I'll leave that up to them. I just progress one day at a time and go from there.

"Obviously I want to come back as soon as possible, but I don't want to rush anything right now. All I can do right now is cheer and root for the team to do good things. It's a good feeling to be on a good start like this."

Paxton placed on DL; Mariners call up Luetge

SEATTLE -- Rookie left-hander James Paxton was placed on the 15-day disabled list Wednesday as the Mariners recalled reliever Lucas Luetge to take his place on the 25-man roster.

An MRI on Wednesday confirmed Paxton strained the lat muscle behind his left shoulder during Tuesday's 5-3 victory over the Angels, when he was taken out of the game with none out in the top of the sixth after throwing his 60th pitch of the night.

The 25-year-old said he's not sure when he'll be allowed to begin throwing again, as trainers are putting together a rehab plan.

"We're kind of still in the assessment stage right now," said Paxton, ranked as Seattle's third-best prospect. "We'll re-evaluate after those 15 days and see where I'm at. I wasn't sore this morning and my strength was really good. I was feeling pretty good about it, but we just want to be careful with it right now."

Paxton is 2-0 with a 2.25 ERA in two starts this year and 5-0 with a 1.75 ERA in six career starts after coming up last September.

"It's tough," he said. "I was feeling good out there. It's not the ideal situation, but I'm just going to deal with it and get ready to go."

Manager Lloyd McClendon said veteran right-hander Chris Young will take Paxton's spot in the rotation for Sunday's series finale with the A's at Safeco Field.

Young is the Mariners' fifth starter but was moved temporarily into a long-relief role when his start was skipped due to postponement of last Friday's game in Oakland because of poor field conditions.

The Mariners have several options for filling Paxton's spot on a longer basis. Taijuan Walker is making his second Minor League rehab start Wednesday for Double-A Jackson and is close to being ready to return from a Spring Training shoulder issue.

Blake Beavan was also moved up a day to start Wednesday for Triple-A Tacoma.

Luetge, 27, will fill Young's spot in the bullpen for now. The left-hander began the season in Tacoma where he gave up two runs in an inning Sunday in his initial outing. He was 1-3 with a 4.86 ERA in 35 games over three stints with the Mariners last season and is 3-5 with a 4.40 ERA in 98 relief appearances since joining Seattle as a Rule 5 Draft selection in 2012.

Seager feeling better at plate after slow start

SEATTLE -- Even though the Mariners are off to one of their best starts in recent years, Kyle Seager hasn't chipped in much yet with the bat. But manager Lloyd McClendon said the 26-year-old third baseman is the least of his worries.

Seager was hitting .158 going into Wednesday's game with the Angels, but he doubled and walked three times in four plate appearances in Tuesday's 5-3 victory and said things are coming together at the plate.

"Things are starting to feel better," Seager said. "I've been seeing the ball a little better the last couple days. I'll try to keep it going."

The young third baseman has been one of the Mariners' most consistent players since getting called up in 2011. He hit .259 and .260 the past two years with 20 and 22 home runs. He led the club with 86 RBIs in 2012 and had 69 last year, with a .423 slugging percentage in 2012 and .426 in '13.

So despite Seager's .191 batting average in Spring Training and his slow first week in the regular season, McClendon remains unconcerned.

"He's a pro," McClendon said. "He's proven it and it's in the books. I really didn't worry about him in Spring Training. I just wanted to make sure he got his work in. If I've got to worry about Kyle Seager, then I'm in trouble, I probably need to quit this job."

McClendon said he admired Seager's play from the opposite dugout the past few years as the Tigers' hitting instructor.

"I noticed him right away. He had quality at-bats," McClendon said. "He hung in there against left-handers, caught the ball at third. He's just a solid baseball player that you tend to notice. He's very professional, very regimented. He knows what he's doing and what he needs to do to get ready. And that's pretty impressive for a young player. He's not afraid of work and he's thirsty for knowledge. The combination of all those things make him pretty good."

Worth noting

• When Corey Hart hit a pair of home runs Tuesday, he became the first Mariner ever to record two homers in his first game at Safeco Field. Hart never played in Seattle during his 10 years with the Brewers.

• The Mariners had the lowest bullpen ERA in the American League at 2.08 after Tuesday's four innings of shutout relief. Seattle's starters ranked fifth in the AL with a 2.98 ERA and second in opponent's batting average at .201 going into Wednesday's games.

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.