WINSTON-SALEM, N.C. (AP) Second-seeded Kevin Anderson of South Africa beat eighth-seeded Borna Coric of Croatia 6-2, 7-6 (1) on Thursday night to advance to the semifinals in the Winston-Salem Open.

Anderson, ranked 15th, will face 88th-ranked Malek Jaziri of Tunisia, a 6-3, 6-2 winner over sixth-seeded Thomaz Bellucci of Brazil.

Anderson had 10 aces Thursday in improving to 6-0 this season in quarterfinal matches, broke the 18-year-old Coric's serve twice and converted 85 percent of his first serves in winning the first set.

''I really played well today, especially in that first set,'' Anderson said. ''It was one of those sets where everything was coming off my racket nicely, I was taking care of my service games and putting myself in each return game. When I'm able to do that, I play my best and make it as tough as possible for my opponent.''

The two were even on serve in the second set to force the tiebreaker, but Coric misplayed a volley at the net with the score tied 1-1, giving Anderson the lead and beginning a run of six consecutive points to close out the match.

''It was a bit of a tricky shot,'' Anderson said. ''Out of 100 times, you're going to maybe win that once. I got a little bit lucky on that point, but it went from 2-1 suddenly to 4-1. That gave me a bit more of confidence. Obviously, you never know what's going to happen, but as things turned out, it was in my favor going up that early.''

American Steve Johnson advanced when Taiwan's Yen-Hsun Lu withdrew because of a back injury. Johnson, seeded 13th and ranked 49th, will play French qualifier Pierre-Hugues Herbert.

Lu was hurt late in the third set Wednesday in his 7-6 (1), 1-6, 7-5 victory over South Korea's Hyeon Chung. He was treated after the match and Thursday morning, but the pain and cramping persisted during practice.

''There's a disk that had some inflammation inside, and the inflammation got into the muscle and got it tight,'' Lu said. ''It was really affecting my serve. We're all looking forward to next week, but I'm still upset.

''We did everything we could with the ATP (trainers). There's still some soreness, and I really couldn't do anything natural. It really didn't make sense to go on the court and play. It's not smart.''

Johnson reached his third career semifinal and second this season. The two-time NCAA champion at South California made his last semifinal appearance three weeks ago in Washington.

''It's never the way you want to win,'' Johnson said. ''Rendy's (Lu's nickname) a great competitor, and I was looking forward to getting a chance to play. Unfortunately, for him, his back isn't feeling 100 percent. With the U.S. Open right around the corner, he didn't want to jeopardize something today for the following week. Now I just take today, and get ready for tomorrow.''

Herbert, ranked 140th, beat Pablo Carreno Busta of Spain 4-6, 7-6 (5), 6-2 to reach his first semifinal.

Jaziri advanced to the semifinals in an ATP World Tour event for the first time this season and the second in his career. His last semifinal appearance came in Moscow in 2012.