Coco Gauff dealt just fine with the heat, the humidity, her big-hitting opponent and the task of trying to reach the U.S. Open semifinals for the first time, defeating 2017 French Open champion Jelena Ostapenko 6-0, 6-2 on Tuesday. Gauff, a 19-year-old from Florida, is the first American teenager to reach the final four at Flushing Meadows since Serena Williams was the runner-up to her older sister, Venus, in 2001. “Last year, I lost in the quarterfinal stage, and I wanted to do better this year,” Gauff said.