The southpaw has pitched effectively for the White Sox this season, posting a 3.04 ERA over 26 2/3 innings pitched. Thornton has been a staple out of the Chicago bullpen for the past eight seasons, and owns a career 3.49 ERA.
The 36-year-old is not as dominant as he used to be, as he has seen his strikeouts fall in each of the past three seasons. Thornton posted a career-high 12.02 K/9 in 2010, but owns a 6.75 K/9 in 2013. The White Sox have utilized the lefty in a more situational role this season; Thornton has thrown less than one inning in 22 of his 38 appearances this year.
Boston entered Sunday's game with the highest bullpen ERA in the AL East at 4.12. Left-handed pitcher Andrew Miller, who has been one of the team's more effective relievers, exited Saturday night's loss against the Toronto Blue Jays with a left foot injury, per Evan Drellich of MassLive.Com.