“For the first time in a while, my nerves really got the better of me, and it kind of became a little bit paralyzing,” Keys said after the match. “I felt like I was just slow. I wasn’t seeing things the way that I wanted to, which I feel like resulted in a lot of bad decisions and lazy footwork.”

Madison Keys admitted nerves "paralyzed" her in New York as she suffered an unexpected US Open first-round defeat to unseeded Renata Zarazua.

American Madison Keys couldn't overcome unforced errors and double faults as Renata Zarazua made Mexican women's tennis history at the U.S. Open.

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.

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.