(AP Photo/Paul White)

MADRID (AP) Dominic Thiem capitalized on two of his four chances to break John Isner's serve, and that was all he really needed.

Thiem was able to break the tall American on his first chance in the second set and then once more in the third, defeating Isner 3-6, 6-3, 6-4 Friday to reach the semifinals at the Madrid Open for the fourth straight time.

"He is one of the best servers in history, especially here in the altitude. His serve is bouncing so high and it's so difficult to return," Thiem said. "I really stayed focused, with a good fighting spirit. Against guys like him, a few points decide and that's when I saved the break points in the beginning of the second set."

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