Complex sentence: At the 2014 Summer Youth Olympics in Nanjing, Xu won the gold medal in Mixed Doubles, partnering Jan Zieliński defeated Ye Qiuyu of China and Jumpei Yamasaki of Japan 4--6,6--3, (10--5) in the final.
Split into simpler sentences: At the 2014 Summer Youth Olympics in Nanjing, she won the gold medal in Mixed Doubles, partnering Jan Zieliński. They defeated Ye Qiuyu of China and Jumpei Yamasaki of Japan 4--6,6--3, (10--5) in the final.