Masterson, 30, has made seven starts with Boston this season, going 2-2 with a 6.37 ERA (25 ER/35.1 IP) and 24 strikeouts. He last started on Tuesday night in Oakland, allowing six runs on six hits and one walk in 2.1 innings. The right-hander ranks 16th in the American League with a 51.3 ground ball percentage and has held opponents to three or fewer runs in four of his seven games started. In 247 career appearances (182 starts) between the Red Sox (2008-09, 2015), Indians (2009-14), and Cardinals (2014), he has combined to go 62-74 with a 4.31 ERA (563 ER/1,177.0 IP) and 979 strikeouts.
Ross, 25, is making his second major league stint of 2015 after beginning the season on Boston's Opening Day roster. The left-handed reliever made 13 appearances with the Red Sox, including eight scoreless outings, and posted a 6.17 ERA (8 ER/11.2 IP) with no record, four walks, and seven strikeouts prior to being optioned on May 10. He saw action in one game with Pawtucket on May 11 against Indianapolis, allowing one run in two innings pitched. Ross, who was acquired via trade from the Texas Rangers on January 27, has gone 13-8 with a 4.10 ERA (99 ER/217.1 IP) and 163 strikeouts in 163 career major league games (12 starts) between the Rangers (2013-14) and Red Sox (2015). As a reliever in the big leagues, he owns a 12-2 record and 3.49 ERA (61 ER/157.1 IP) with 121 strikeouts in 151 appearances.