Day two of the US Open delivered the tournament’s first big stunner. Renata Zarazúa of Mexico defeated No. 6 seed Madison Keys 6-7(10), 7-6(3), 7-5 in a major first-round upset at Arthur Ashe Stadium Monday afternoon.

Australian Open champion Madison Keys was undone by 89 unforced errors and was upset in the first round of the U.S. Open by Renata Zarazua of Mexico.