Steve Johnson reached the Winston-Salem Open semifinals because of a back injury to Taiwan's Yen-Hsun Lu.
Lu was hurt late in the third set of Wednesday's quarterfinal, which he lost 7-6 (1), 1-6, 7-5 to South Korea's Hyeon Chung at the Wake Forest Tennis Center. He was treated after the match and on Thursday morning. The pain and cramping persisted during practice, forcing his withdrawal.
Johnson is seeded 13th and the lone American remaining. He next plays either qualifier Pierre-Hugues Herbert of France or Pablo Carreno Busta of Spain.
In the evening session of this tuneup for next week's U.