World number one Arina Sabalenka of Belarus easily defeated China’s Qinwen Zheng in a group stage match at the WTA Finals on Saturday with a 6-3, 6-4 victory in Riyadh, Saudi Arabia. Sabalenka finished with just three aces compared to eight for Zheng, but she won 31 of 33 first-serve points and battled back after losing 1-0, 2-1, 3-2 and 4-3 in the second set.