Iwakuma turned down Seattle's one-year, $15.8 million qualifying offer, becoming a free agent. After a number of the top available starters -- David Price, Zack Greinke, Jordan Zimmermann, Jeff Samardzija and John Lackey -- came off the board in recent days, Iwakuma's name surged to the fore of much speculation as executives from all 30 Major League teams began gathering Sunday at the Opryland Hotel on the eve of the four-day Winter Meetings.
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Both the Dodgers and Giants were reportedly pursuing Iwakuma on Sunday, looking to finalize deals before the Meetings began.
Because the Mariners made Iwakuma a qualifying offer, they will receive a compensatory pick at the end of the first round of next June's Draft if he does sign elsewhere.
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Iwakuma has quietly been one of the American League's top right-handers the past four years, posting a 47-25 record and 3.17 ERA with a 1.08 WHIP. Though he missed 10 weeks with a strained lat muscle last season, he still went 9-5 with a 3.54 ERA and threw a no-hitter against the Orioles in August.
The Mariners have ace Felix Hernandez atop their rotation, with promising 23-year-old Taijuan Walker coming off a strong first full season in the Majors and highly regarded left-hander James Paxton trying to get healthy after two injury-plagued seasons. Dipoto added Rays right-hander Nathan Karns via a trade last month, and the club also has lefties Vidal Nuno and Roenis Elias returning (both have Minor League options). Mike Montgomery also returns, though he's out of options and thus provides less roster flexibility.
Dipoto would like to bolster that group with a quality veteran like Iwakuma, who has been Seattle's No. 2 or 3 starter since moving into the rotation in mid-2012, after signing with the Mariners following an outstanding 11-year career in Japan.
Iwakuma was an AL All-Star in 2013 and finished third in the AL Cy Young Award voting that season after going 14-6 with a 2.66 ERA. Age and durability are the main questions regarding Iwakuma, who missed the first month of 2014 with a strained finger tendon and was sidelined last year by the lat strain.
If he does go elsewhere, the Mariners will almost certainly turn toward other remaining free-agent pitchers or pursue the trade market for a replacement.
Johnny Cueto is the biggest name remaining among the free-agent arms, though he figures to be in the blockbuster category that Dipoto has indicated the Mariners wouldn't be pursuing. Other prominent free-agent pitchers include Mike Leake, Wei-Yin Chen, Scott Kazmir, Ian Kennedy, Yovani Gallardo, Mat Latos, Doug Fister, Mark Buehrle and Bartolo Colon.