The Athletics recalled Hartlieb from Triple-A Las Vegas on Saturday, Martin Gallegos of MLB.com reports.
With Mark Leiter (hip) headed for the injured list, the A's will turn to Hartlieb to plug the hole in their bullpen. The 32-year-old righty has spent the entire season at Las Vegas, posting a 3.48 ERA and 1.39 WHIP across 33.2 innings in the hitter-friendly Pacific Coast League. He's likely set for middle-relief work as long as he's in the majors.