American juniors are continuing their success at the world's biggest tournaments, as 17-year-olds Claire Liu of Thousand Oaks, Calif., and Ann Li of Devon, Pa., have advanced to the semifinals at junior Wimbledon.

Playing for the first time at the All England Club this year, Li (pictured above) advanced to the final four with a stunning upset over 2016 US Open girls' champion, top seed and fellow American Kayla Day, 4-6, 6-2, 6-1. She will meet Simona Waltert of Switzerland in the semifinals.

No. 3 seed Liu, the 2016 Wimbledon girls' doubles champion (with Usue Arconada) and a finalist at this year's junior French Open, ousted No. 6 Carson Branstine of Canada, 4-6, 6-1, 6-1, to reach the semis. She will take on Sofya Lansere of Russia for a spot in the final.

If Liu and Li both win their next matches Friday, they would square off in the first all-American girls' final at Wimbledon since 1979, when Mary Lou Piatek defeated Alycia Moulton for the title. ADVERTISEMENT It would also be the second consecutive all-American girls' Grand Slam singles final, after Whitney Osuigwe defeated Liu to win the French Open junior title last month.

Overall, it has been a good tournament for American girls at Wimbledon, with five of the eight quarterfinalists hailing from the U.S. – Liu, Li, Day, Osuigwe and No. 14 seed Sofia Sewing.

On the boys' side, North Carolina native Patrick Kypson, 17, advanced to the quarterfinals Thursday with a 4-6, 6-0, 8-6 win over Britain's George Loffhagen. He will next take on Michael Vrbensky of the Czech Republic in the quarterfinals.