There are three American men aged 23 and under in the second week of a Grand Slam. That hasn't happened since 2003

Two friends from California, Learner Tien and Alex Michelsen, have both reached the fourth round at the Australian Open. Tien is 19, and Michelsen is 20.

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?

The 19-year-old American upset fifth-seeded Daniil Medvedev in a five-set Australian Open marathon that lasted nearly five hours.

Learner Tien has become the youngest American man to reach the Australian Open’s third round since Pete Sampras in 1990.

Two of four American men still playing in Melbourne, Irvine native Tien, 19, and Aliso Viejo native Michelsen, 20, became friends on the youth tennis circuit