BEIJING–Belgium’s Elise Mertens beat Poland’s Iga Swiatek 7-6 (7/0), 6-3, in the China Open on Friday and advanced to the semifinals against hometown bet Zheng Qinwen. Mertens, the world number 19, overcame some nerves to dump out Swiatek, the 2023 title winner. “I tried to be consistent. She’s a great player, so I had to