Coco Gauff was upset Monday at Arthur Ashe Stadium by Naomi Osaka in the Round of 16 at the U.S. Open, and she admitted to reporters that it was a tough loss to handle emotionally.Gauff said she "kind of broke down" to her team after falling 6-3, 6-2 in a shocking performance for the No. 3-ranked American star."After the match, I was really disappointed," Gauff explained. "Kind of broke down to my team. Then, hearing their perspectives and everything, it definitely is a lot of positive things. I think if I kept the way I was going in Cincinnati to her, I would have been out in the first round. So, I think where my serve started from the start of the tournament to today was a big improvement."CLICK HERE FOR MORE SPORTS COVERAGE ON FOXNEWS.COMBefore the final Grand Slam of the tennis season began, Gauff made a big coaching change, parting ways with Matt Daly and bringing in biomechanics expert Gavin MacMillan.The move was specifically done to help correct Gauffs serve, and MacMillan has worked with some of the best in the game, including top-ranked womens singles player Aryna Sabalenka, to get their serves right.AMERICAN TENNIS STAR COCO GAUFF MAKES MAJOR CHANGE JUST DAYS BEFORE US OPENSo, while that area of Gauffs game felt improved in her eyes, she committed 33 unforced errors that were hard to overcome against Osaka, the two-time U.S. Open champion and No. 23-ranked player in the tournament this month.Moving forward, Gauff knows that she and her team must focus on rounding out her game once again."I feel like now I just have to get everything to work together," she added. "But yeah, I knew going in it was going to be a tough tournament for me. Did I feel like I had a lot of confidence after my last match? Yeah, definitely. I think that was a big confidence booster. So today feels more disappointing, I think, than maybe it would have felt losing in the first or second round."Meanwhile, Osakas game has been fun to watch in Flushing Meadows since the tournament began, as the 2018 and 2020 U.S. Open champion is riding high after defeating her friend Gauff."I was super locked in," she said of her performance during the win. "I felt like everyone wanted to watch a really great match and I hope thats what you got."This is Osakas first trip to the quarterfinals at a Grand Slam since she won the Australian Open in 2021. She has dealt with mental health struggles in the past, bravely speaking up about them and taking a break from the sport as a result.Osaka gave birth to her daughter, Shai, in 2023, which led to an absence from the court.Osaka moves on to face No. 11 Karolna Muchov in the quarterfinals Tuesday.Follow Fox News Digitalssports coverage on X, and subscribe tothe Fox News Sports Huddle newsletter.