McCullers (4-2) permitted just one run on five hits and a walk with 10 strikeouts over seven innings during Monday's win over the Mariners.
It was McCullers' sharpest outing of the season and the first time this year that he's permitted fewer than three walks during a start. The 22-year-old right-hander will carry a 3.57 ERA into his next scheduled start Saturday against the A's.