The Pirates' decision to summon two relievers -- the team's other roster vacancy was created when Zach Duke was placed on the disabled list -- appears dictated by the need to have some fresh bullpen arms available for the next few days.
Manager John Russell had to use five relievers on Wednesday, and the bullpen has logged 17 innings in the past four days.
This will be Jackson's second go-round with Pittsburgh this season. He made one relief appearance (May 28) during that previous short stint. In 22 games with Triple-A Indianapolis this season, Jackson has allowed 10 earned runs on 34 hits and 11 walks in 31 innings. He has struck out 18. Jackson has not allowed a run in his past 10 Triple-A appearances, though he did recently miss two weeks after being struck in the arm by a line drive.
This will be Thomas' first return to the Majors since 2008, when he went 0-1 with a 6.75 ERA in eight relief appearances for the Mariners. Thomas, 26, is 3-0 with a 1.30 ERA in 24 relief appearances with Indianapolis. He has allowed just two earned runs in his past 19 appearances.
As for Eveland, his problems on Wednesday ended his brief time in Pittsburgh. The left-hander allowed six earned runs on seven hits and two walks in 2 2/3 innings against the Rangers and complained afterward of getting tired because of the heat.
Cumulatively, Eveland allowed nine earned runs on 15 hits in 9 2/3 innings with Pittsburgh. He was acquired on June 1 in a deal that sent Minor League right-hander Ronald Uviedo to Toronto.
Jenifer Langosch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.