Pretty much from the get-go Monday at the U.S. Open, Madison Keys could tell she wasn’t hitting the ball well or feeling very much at all like the self-confident player who won her first Grand Slam title at the Australian Open in January.

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

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.