In her short time at the highest level, Coco Gauff has built a glittering career on grit and perseverance, possessing a rare ability to find a way to win even when she’s not playing at her best. But deep into the third set against Emma Navarro, defending her US Open title, not even her fighting spirit could mask the gaping cracks in her game.

A year after becoming a Grand Slam champion on the same court, Gauff left Arthur Ashe Stadium after a poor performance in the fourth round of the US Open. The ingenuity and nerves of the ever-solid Navarro helped her advance to the quarterfinals on home soil for the first time in her career with a 6-3, 4-6, 6-3 victory.

With another important win, Navarro cements her status as one of the most improved players on the tour. The 23-year-old American has now defeated Gauff in two consecutive Grand Slam tournaments, having also won the fourth round at Wimbledon to reach her first Grand Slam quarterfinal.

“I think we both had our own issues at times,” Navarro said. “I think it was a little bit of a battle of wills for a while. But I was proud of my performance today. I was able to persevere in some difficult moments.”

During her two hours and twelve minutes on court, Gauff was excruciating to watch as she struggled with elemental aspects of her game. Her performance underscored long-standing issues that must be addressed if she is to repeat her results from last year and win another Grand Slam title.

Gauff’s forehand couldn’t withstand the sustained pressure from Navarro and then her serve failed, especially in the final set. She finished the match with a miserable 19 double faults, 11 of them in the final set alone, and her forehand made 29 unforced errors compared to just five winners. This defeat ended a difficult summer for Gauff, in which she already lost in the round of 16 at Wimbledon, at the Olympic Games and now at the US Open.

“I gave it my all mentally and emotionally,” said Gauff. “Of course there were things I found fault with in the execution, things I wished I could have served better. I think if I had done that, the match would have turned out very differently for me. But Emma played really well. I thought she did everything well.”

Navarro, seeded 13th, is an inventive, efficient player who moves well, has adopted a more attacking mindset to compete at the highest level and has few weaknesses in her versatile game. She picked up where she left off at Wimbledon by being solid on both groundstrokes, maintaining excellent depth and getting her backhand up high well.

That depth and consistency that Navarro displayed immediately exposed Gauff’s inconsistent forehand, and Navarro quickly built a 6-3, 4-3 lead with a break in the second set. Gauff used her mental strength to win three games in a row and force a final set, but when Navarro shook off her nerves and stayed consistent until the end, Gauff’s serve capitulated throughout the final set. She spent the rest of her evening at Arthur Ashe Stadium struggling and failing to keep her serve between the lines.

After a hugely successful college career, Navarro, the daughter of billionaire businessman Ben Navarro, enjoyed her first full year as a professional tennis player just last year. She has risen quickly and could break into the top 10 based on her results this week. Although she has already exceeded her wildest expectations, her rise is far from over.

“When I left college, my coach and I signed a two-year contract where I committed to playing professional tennis for two years and then re-evaluate after that. I think I hit the two-year mark this June and we didn’t even acknowledge it or talk about it,” she said. “So I definitely exceeded my expectations. I hope I just keep getting better.”

In her first US Open quarterfinal, Navarro will next face former Spanish No. 2 Paula Badosa, who bounced back from a career-threatening back injury to reach her second Grand Slam quarterfinal with a 6-1, 6-2 victory over China’s Wang Yafan. Both Navarro and Badosa were born in New York City.

Ninth seed Grigor Dimitrov held his nerve to beat sixth seed Andrey Rublev 6-3, 7-6(3), 1-6, 3-6, 6-3 to reach the US Open quarterfinals for the first time in five years. Twelfth seed Taylor Fritz recovered from a set down to beat eighth seed Casper Ruud 3-6, 6-4, 6-3, 6-2.

Meanwhile, Jack Draper believes he is putting himself in position to challenge for the world’s biggest titles in the coming years, at a time when the next generation of tennis players are starting to make their mark at the big events.

“I believe that if I stay injury free, continue to work hard on my body and take the experience I gain from playing week in and week out, I have a great opportunity. I am confident that I can make it to the top level,” said Draper.

Draper will make his second consecutive fourth round appearance at the US Open when he faces Tomas Machac of the Czech Republic on Monday, with both players seeking their first Grand Slam quarterfinals.