Hernandez, 23, has appeared in two games this season over two stints with the Red Sox, the first of his Major League career. The Dominican native made his big league debut on April 17 against the Toronto Blue Jays, starting at second base and going 1-for-2 with a walk, a stolen base, and a run scored. He also appeared in a game against the New York Yankees on April 30, entering as a defensive replacement at second base in the eighth inning. In 24 games with Pawtucket this season, the left-handed batter has hit .333 (31-for-93) with a .386 on-base percentage, five doubles, one triple, and one home run. Hernandez has made 11 starts at second base, eight at shortstop, and three at third base, also starting one game in left field. Over seven Minor League seasons between the Chicago Cubs (2010-14) and Red Sox (2015-16) organizations, he has hit .282 (650-for-2,305) with 116 doubles, 30 triples, 27 home runs, and 264 RBI in 601 games.
O'Sullivan, 28, made three appearances (two starts) for the Red Sox in his only stint with the club, going 1-0 with a 7.94 ERA (10 ER/11.1 IP). The right-hander started yesterday's series finale against the Houston Astros but did not factor into the decision, allowing six runs-five earned-in 4.1 innings. Signed by the Red Sox as a Minor League free agent on December 5, 2015, O'Sullivan has also made five starts at Pawtucket this season, going 2-2 with a 3.00 ERA (11 ER/33.0 IP) and 32 strikeouts against five walks. Originally selected by the Angels in the third round of the 2005 June Draft, he is 12-23 with a 6.03 ERA (210 ER/313.2 IP) in 69 games (54 starts) over parts of seven Major League seasons with the Angels (2009-10), Royals (2010-11), Padres (2013), Phillies (2014-15), and Red Sox (2016).