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 Daniil Medvedev in five sets Thursday.

At the age of 19, Learner Tien defeated Daniil Medvedev in a five-set thriller that finished just before 3 a.m. in Melbourne.

Daniil Medvedev is out of the Australian Open after losing to American qualifier Learner Tien in the biggest upset of the tournament so far. The 28-year-old was taken all the way to a deciding set by his teenage opponent, with the match going on for nearly five hours and ending just before 3:00am.