Claire Liu, the No. 3 seed from Thousand Oaks, Calif., defeated the unseeded Ann Li, of Devon, Pa., 6-2, 5-7, 6-2.
The last junior girl from the United States to win the event was Chanda Rubin in 1992, when Venus Williams was only 12. But there are indications that the United States is making progress among its female juniors.
Wimbledon was the second consecutive Grand Slam girlsâ final between two Americans. Last month, Liu lost to Whitney Osuigwe, currently the top-ranked junior girl in the world, in three tough sets at the French Open.
And Kayla Day, who was the No. 1 seed here, won the United States Open junior event in September, defeating Viktoria Kuzmova of Slovakia in straight sets.
At Wimbledon, there were five Americans in the quarterfinals, including Sofia Sewing, Osuigwe, Liu and Day, who was upset by Li.
Liu trains at the United States Tennis Associationâs facility in Carson, Calif., and there has been a belief among top U.S.T.A. coaches that she would become the best of the group. She also won two clay-court Pro Circuit titles in Italy before Wimbledon.
Sam Querrey, who made it to a semifinal of the menâs draw, is also from Thousand Oaks and said he frequently saw Liu at the training center in Carson.
âIâm stoked for her,â he said. âSheâs really good.â
Liu said that training with the other young women in Carson, and also on tour with other players in the U.S.T.A. training program, has been beneficial because it spurs the competition in a teamlike atmosphere.
âWe are all pretty good friends,â she said. âWe try to train together a lot with the U.S.T.A. Itâs really good to have a good group of juniors pushing each other.â
Liu is not physically imposing like the Williams sisters, or GarbiÃ±e Muguruza, who beat Venus in straight sets in the womenâs final on Saturday. But Liu plays aggressively, takes the ball early to attack her opponent and comes to the net, where her volleying is strong.
Osuigwe, the daughter of a coach, trains at the I.M.G. Academy in Bradenton, Fla. She is No. 1 in the International Tennis Federationâs junior rankings for now, and Liu is No. 2. Li trains at the U.S.T.A. center at Flushing Meadows. She does not have the pedigree of the others, but she showed great competitive grit Saturday, fighting off four match points before finally succumbing.
âThe crowd was getting into it, and that kind of got me going,â Li said. âI was pretty nervous at first.â
The match was played in front of a healthy contingent of fans on No. 1 Court at the same time as Muguruzaâs surprisingly easy win over Williams. At times during the match, the sounds of people cheering outside while they watched the womenâs final on a large video screen could be heard, and when the unexpected scores were flashed inside the stadium, spectators gasped.
Liu won the first set easily, then served for the match at 5-4. She was up, 40-0, but then nerves began to rattle her play. She hit a backhand long and sighed, and then double-faulted. At 40-30, Li rocketed a forehand passing shot to get the game to deuce, and she eventually won the game with a blistering backhand.
After Li won the next game to make the score 6-5, Liu complained to the chair umpire about the last disputed point of the game and argued for the entirety of the changeover. She did not even sit down, instead standing in front of Li to question the umpire.
âI was just trying to mind my own business,â said Li, who broke Liu again to close out the second set in a thrilling game with five deuces.
But in the third set, Liu recaptured the flow, getting low to the grass while firing groundstrokes to break Li in the first game. When Liu won the match, she dropped her racket and fell onto her back in a celebration that she did not want to end. Her plan was to go to an Indian restaurant with friends.
âI just keep smiling all the time,â she said. âI still canât even believe it.â
DOUBLES CHAMPIONS CROWNED Lukasz Kubot and Marcelo Melo won the menâs doubles title, beating Oliver Marach and Mate Pavic, 5-7, 7-5, 7-6 (2), 3-6, 13-11.
The match lasted 4 hours 40 minutes, only 21 minutes shorter than the longest Wimbledon menâs doubles final in history. It ended under a closed roof because of darkness.
With Saturdayâs win, Melo, a Brazilian, will return to the No. 1 ranking in menâs doubles.
Both players won their second Grand Slam titles. Melo won the 2015 French Open with Ivan Dodig. Kubot won the 2014 Australian Open with Robert Lindstedt. (AP)