The 30-year-old Blackley went 1-1 with a 4.89 ERA in 42 relief appearances for Houston this season before being designated for assignment on Aug. 8. He cleared waivers and accepted an outright assignment to Triple-A Oklahoma City and joined the RedHawks on Tuesday.
Blackley will not be on the 40-man roster and has been assigned to Triple-A Round Rock.
The Australian is 8-8 with a 5.28 ERA in 78 career games, including 23 starts. Four of his eight career wins have come against the Rangers.
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