"We needed a pitcher for [Tuesday night's] and [Wednesday afternoon's] games," said manager Clint Hurdle, citing the pair of games the Bucs would be playing against the Giants in a 20-hour window. "He fit the criteria of what we needed. It's an opportunity for him to give us some length. He's pitched well the last few times out after a rough start."
Irwin missed most of Spring Training with a tender elbow and allowed 17 runs in 8 2/3 innings in his first four outings for the Indians, including two starts. In his last three relief appearances, he allowed one run in 9 1/3 innings.
He made one appearance for the Pirates last year, a start in which he allowed four earned runs without escaping the fifth inning.
Locke, an All-Star last season, made one start for the Bucs in 2014, allowing eight hits and six earned runs over 5 1/3 innings Monday.
Locke made 30 starts for Pittsburgh last year, logging a 10-7 record with a 3.52 ERA. The 26-year-old has made four starts for Indianapolis this season, going 0-1 with a 5.68 ERA.