And, yeah, it's been a long haul for the 33-year-old from Japan, who finished third in the American League Cy Young Award voting last year and then immediately said he wanted to improve on that season.
"I look forward to tomorrow," Iwakuma said Friday, speaking through translator Antony Suzuki. "It's been a long wait. I've always wanted to be part of the team soon and contribute, so that said, it's a very exciting day for me."
It's a welcome day as well for the Mariners, who have had Iwakuma, James Paxton, Taijuan Walker and Blake Beavan all on the disabled list for most of the first month of the regular season. With help from rookie Roenis Elias and veteran addition Chris Young, they've cobbled things together as best as possible behind ace Felix Hernandez.
Seattle's starters have gone 9-7 and rank fifth in the AL with their 3.70 ERA through the first 26 games despite getting just two starts from Paxton, one from Beavan and none from Walker. But there's no question they'll be boosted greatly by the return of Iwakuma, who was their most productive starter last year, when he went 14-6 with a 2.66 ERA in 33 starts.
"Anytime you can go back-to-back All-Star pitchers in your rotation, that's pretty good," said manager Lloyd McClendon, who finally has Iwakuma following Hernandez in the rotation. "Obviously that's going to be a big lift for us."
The Mariners had won five of their last six games and were coming off two straight wins against the Yankees as they arrived in Houston, so Iwakuma figures the timing is perfect for his return.
"We have momentum on our side, and hopefully I can get on top of that and kind of go on a roll," he said.
The Mariners will need to make a move Saturday to add Iwakuma to their 25-man roster. McClendon said the likely scenario would be to send a reliever down to Triple-A Tacoma, as the club is currently carrying an extra bullpen arm after promoting Lucas Luetge when Erasmo Ramirez was sent down last week.
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.