A career year for Madison Keys ended in a Grand Slam shock.

Mexico’s Renata Zarazua may have been the opponent on the other side of the net, but the No. 6-seeded Keys got in her own way and committed an astounding 89 unforced errors to bow out in the first round of the U.S. Open 6-7(10), 7-6(3), 7-5 Monday afternoon.

“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.”

Zarazua rallied from a set and 3-0 down to stun Keys on a sun-drenched Arthur Ashe court, earning the world No. 82 her first victory over a top 10 player after previously going 0-6.

As the only Mexican player in the singles draw, Zarazua became the first woman from her country to defeat a top 10 seed at a Grand Slam since Angelica Gavaldon took down Jana Novotna at the 1995 Australian Open.

The monumental loss for Keys made some history of its own, with the 30-year-old standing as just the second American woman seeded in the top 10 to lose in Round 1 of the U.S. Open in the past 30 years.

“I just feel like from pretty early on in the first set, it was pretty apparent that I wasn’t playing great tennis today,” she said.

Keys, who topped the Australian Open in January to capture her first Grand Slam title, admitted to having some pretournament jitters leading up to the competition in Flushing.

Perhaps there was some added pressure coming into the high-profile New York event as a first-time Grand Slam champion.

Perhaps it weighed even heavier after she reached her career-high ranking of No. 5 in February.

The nerves appeared to be crippling for Keys, who made mistake after mistake.

With her left thigh heavily taped, Keys committed 14 double faults to Zarazua’s five. Zarazua needed just eight winners to secure the biggest victory of her career.

“You always kind of feel first-round jitters, and as the day is getting closer, feeling a little bit more and more nervous. But I feel like for whatever reason, today, I just couldn’t separate myself,” said Keys, who was runner-up at the U.S. Open in 2017. “And it’s more than just saying, ‘I want to win,’ but just feeling like winning matters just way too much, and I just couldn’t quite separate myself from that. Then once you start playing badly, it just kind of all snowballs.”

After the first set ran some 72 minutes and featured nine set points, Keys emerged on top following a 22-point tiebreak. Of those nine set points, five of them belonged to Zarazua, but Keys ultimately saved them all.

Zarazua then erased a 3-0 deficit by taking five straight games in the second set before evening the match up at one set apiece with her own tiebreak victory. The 27-year-old then broke Keys at 6-5 in the final set to advance to the second round, where she’ll face Diane Parry on Wednesday.

The 5-foot-3 Zarazua had lost in either the first or second round in all eight of her previous Grand Slam appearances. She’s never advanced past the second round before.

“I think it’s a country that we don’t have many tennis players, as you can see,” Zarazua said during her on-court interview after making her Arthur Ashe debut. “But I had some of the Mexican tennis from doubles cheering for me. We just tried to give our best. Definitely, I could hear some Mexican cheering. That was very nice.”

With Keys out of the way, world No. 3 Coco Gauff’s section of the draw became a little lighter. The two were slated to meet in the quarterfinals had the top seeds in their quarter progressed.