Learner Tien, a 19-year-old qualifier from California, became the youngest American man to reach the Australian Open's third round since Pete Sampras in 1990, upsetting a racket-tossing Daniil Medvedev 6-3,

Learner Tien pulled off a massive upset against Daniil Medvedev at the Australian Open. So, who is Tien, the 19-year-old out of California?

U.S. 19-year old Learner Tien defeated No. 5 Daniil Medvedev in a fifth set tiebreaker in the Australian Open, making history in Melboune.