HOUSTON — The prize for going toe to toe with Astros All-Star pitcher Gerrit Cole? A trip to Nashville.

Frankie Montas was optioned to Triple-A Nashville one day after tossing six scoreless innings in Monday’s 2-0 victory over the Astros. The right-hander has been a revelation for the A’s this season, going 5-2 with a 3.35 ERA over eight starts.

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But the move was not about Montas’ performance.

Trevor Cahill (strained right Achilles) will be activated from the disabled list and slotted into the starting rotation Thursday against the Astros. With the All-Star break approaching next week, the move allows Montas to get a start at Triple-A and continue on his normal rest before returning to the A’s for their road trip in Texas near the end of July.

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Who starts for the Oakland A’s in a three-game postseason series? In the meantime before Cahill is activated, the A’s recalled reliever Ryan Dull from Nashville. After struggling in the majors earlier in the season, Dull has pitched well at Triple-A, posting a 2.51 ERA in 12 appearances with 16 strikeouts over 14 1/3 innings of work, and has posted solid numbers against Houston.

“He’s done OK against some of these guys,” A’s manager Bob Melvin said. “They’ve got a lot of righties so anytime you can get an extra arm that’s got some experience against a certain team, it’s nice to have. And we’ve been using our bullpen quite a bit.”

— Paul Blackburn’s MRI on his right elbow revealed no structural damage, but given that it’s his second arm injury this season, the A’s will shut him down for about two weeks.