Iwakuma's neck tightened up during a pregame training room session prior to his last start Sunday against the Rangers and he wasn't sure he was going to be able to pitch when he was having troubles warming up in the bullpen, but wound up throwing eight innings of one-run ball in a 5-1 victory.
Iwakuma skipped his usual bullpen session between starts this week, but did play flat-ground catch both Tuesday and Wednesday.
Manager Lloyd McClendon didn't expect any problems for Friday's matchup against Royals ace James Shields in the first game of a three-game set in Kansas City.
"He's going to make his start," McClendon said. "He's not 100 percent, but he's ready to go unless something drastically changes."
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.