Coco Gauff became the youngest player to win the WTA Finals title in 20 years with a gruelling 3-6, 6-4, 7-6 (7/2) victory over Olympic champion Zheng Qinwen in Riyadh on Saturday. The 20-year-old Gauff rallied back from 3-6, 1-3 down, and erased a one-break deficit twice in the decider, to overcome Zheng in three hours and four minutes – …