Jeff Samardzija is on his way to finishing with his worst ERA since becoming a full-time starter three years ago, and the free-agent-to-be can look back at an especially brutal August if that ends up being the case.

The month had been going extremely well for Hisashi Iwakuma until his latest outing.

Iwakuma looks to help the visiting Seattle Mariners win for the fourth time in five tries as he faces the Chicago White Sox on Saturday night.

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Samardzija (8-10, 4.75 ERA) hasn't finished with an ERA worse than his 4.34 mark in 2012 after the Chicago Cubs made him a regular piece of their starting rotation. That's in jeopardy after he began August by losing his first five starts with a 9.00 ERA.

He allowed at least five runs for the fourth time in that stretch in Monday's 5-4 loss to Boston. Samardzija has lost his last four starts at U.S. Cellular Field with a 9.26 ERA.

''It's been frustrating,'' Samardzija said. ''The last few times out when I've given up runs we've scored runs, and when (I) don't (give up many runs), we don't (score). That sums it up.''

The right-hander's only good start this month was when he went seven innings of a 1-0 loss to the Los Angeles Angels on Aug. 19. The White Sox (60-67) were shut out for the second time in three games Friday, falling 2-0 to the Mariners (60-69).

Melky Cabrera had two hits to improve to 7 for 16 over his last four, and Alexei Ramirez had the other two for Chicago.

''We didn't muster any offense,'' manager Robin Ventura said. ''You have to be able to put something on the board."

Ramirez is 1 for 11 lifetime off Iwakuma (5-3, 4.29), who looks to shake off a rough outing.

Iwakuma went 3-0 with a 1.71 ERA in his first four starts this month, including a no-hitter against Baltimore on Aug. 12. He struggled Monday, though, giving up a career high-tying seven runs in an 11-5 loss to Oakland.

The right-hander cruised through the first four innings and recorded two outs in the fifth, then allowed each run before being removed.

Iwakuma has been solid against the White Sox, going 1-0 with a 1.61 ERA in three starts and two relief efforts. He went seven innings of a 4-1 win the last time he faced Chicago on Aug. 8, 2014.

Seattle has scored two runs in each of the first two of this four-game set, all on homers. Franklin Gutierrez hit a two-run shot in Thursday's 4-2 loss before he and Kyle Seager each homered Friday.

Seager had three hits after going 2 for 28 over his previous seven. Nelson Cruz went 0 for 5, ending his career-high 37-game streak of reaching base as the Mariners stranded 10 runners.

''We were lucky to win,'' manager Lloyd McClendon said.

Robinson Cano is 3 for 4 with two doubles off Samardzija, and Logan Morrison hit his second career homer in their matchups the last time Samardzija faced the Mariners in a 3-2 loss while with Oakland on July 11, 2014.

The Mariners haven't won back-to-back road games against the White Sox since 2007.