Iwakuma, 34, is expected to throw about three innings and 45-50 pitches in the 6:05 p.m. PT game against Eugene at Everett Memorial Stadium.
With Triple-A Tacoma currently on the road in Albuquerque, the Mariners chose to bring Iwakuma back at nearby Everett, which opened its season Thursday. Manager Lloyd McClendon said if all goes well, he expects Iwakuma would make his next rehab start for Tacoma, which returns home next week.
But with the 2013 All-Star sidelined since April 20 when he felt soreness behind his shoulder in his third start of the season, McClendon isn't ready to speculate on how many rehab starts Iwakama will need to make before rejoining the Mariners.