This is winnable match for Kontaveit and I would go even as far as say I would be shocked if she did not take her opportunity here against average player. Most people who did not know much about Kontaveit found out a lot at US Open when she made 4th round.
Make no mistake about it — this girl has got massive game including a monster serve. And she has got some impressive groundstrokes as well. I guess, the only reason why bookies have this as 50/50 match is that Zheng is a local player but she's really quite average player. Kontaveit should win this match and even do so with something to spare. Just too much power and Zheng doesn't have that good of a defense to deal with immense power of Kontaveit.
Kontaveit has already killed three opponents in this tournament including qualies. She is yet to be tested. 6-1, 6-3 smashing of Hsieh, who is better player than Saisai, speaks volumes. Also, Kontaveit just doesn't give much away on serve — she's faced just 5 break points in 3 matches thus far. Has to win this one, she's good enough.