Iwakuma also is coming off his shortest stint of the season, lasting just three frames while allowing seven hits and six runs before Seattle rallied to beat Texas, 8-7.
Iwakuma has extensive history against the A's. The 36-year-old is 9-5 with a 4.14 ERA in 16 games (15 starts) against the American League West rivals and manager Scott Servais said he expects the steady veteran to bounce back strong.
"It had been seven days since he'd last pitched last time," Servais said. "He's on a normal turn now and I know he's anxious to get back out there. He was really disappointed in his outing. Kuma is very quiet, but he's very much a team guy and when it doesn't work in his favor, he feels like he let the team down. So he'll be ready to go."
Things to know about this game
• Iwakuma has struck out just six batters in 15 innings this season, and his declining velocity could be a factor. Of the 141 pitchers who have thrown at least 100 fastballs of any type in both 2016 and '17, none has experienced a larger velocity drop than Iwakuma (86.7 mph to 83.0 mph).
• After sitting out the past two starts against southpaw starters, right fielder Matt Joyce and catcher Stephen Vogt will be back in the lineup against Iwakuma. Joyce has hit .278 (5-for-18) and Vogt .276 (8-for-29 with a double) against Iwakuma.
• Rookie Guillermo Heredia figures to get his fourth start of the season in left field for the Mariners against the lefty Manaea, which probably means Jarrod Dyson will slide over to center and allow Servais to sit Leonys Martin. Martin was batting just .118 with one double and no RBIs heading into Thursday's series opener. Heredia is 4-for-14 with a home run in his limited duty to date.
Greg Johns has covered the Mariners since 1997, and for MLB.com since 2011. Follow him on Twitter @GregJohnsMLB and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.