Zarazua knocked off Australian Open champion Madison Keys, who committed 89 unforced errors and was upset 6-7 (10), 7-6 (3), 7-5 in a first-round match.

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

Australian Open champion Madison Keys has been undone by 89 unforced errors during a 6-7 (10), 7-6 (3), 7-5 loss to Mexico’s Renata Zarazua in the first round of the U.S.