Lu Yen-hsun, of Taiwan, hits a return to Ivo Karlovic, of Croatia, in the semifinals of the U.S. National Indoor Tennis Championships on Saturday, Feb. 15, 2014, in Memphis, Tenn. Lu retired due to injury after losing the first set, 6-1. (AP Photo/Rogelio V. Solis)

Memphis Tennis

Lu Yen-hsun, of Taiwan, hits a return to Ivo Karlovic, of Croatia, in the semifinals of the U.S. National Indoor Tennis Championships on Saturday, Feb. 15, 2014, in Memphis, Tenn. Lu retired due to injury after losing the first set, 6-1. (AP Photo/Rogelio V. Solis)

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