BEIJING–Elise Mertens beat a listless Coco Gauff 6-3, 6-3 on Wednesday to seal her spot in the China Open quarterfinals, where she will face Iga Swiatek. Gauff, the highest-ranked player left in the women’s draw, failed to recover from a series of misjudged shots and double-faulted eight times. It was an uncharacteristically poor showing by