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

MELBOURNE, Australia — Alex Michelson joked that he was too busy at the Australian Open on Saturday morning to have a lengthy phone conversation with his mother back home in California. His excuse was pretty good, actually: The 20-year-old Michelsen was on court for a 6-3, 7-6 (5), 6-2 victory over No. 19 seed Karen Khachanov.

Jannik Sinner continues Australian Open defence with straightforward win; Gael Monfils, 38, dumps out fourth seed Taylor Fritz; American teen sensation Learner Tien also progresses in Melbourne; watch

Stefanos Tsitsipas twice smashed his racket onto his bag as he exited the Australian Open in the first round against young American Alex Michelsen. Tsitsipas, who is enduring a miserable run of Grand Slam form,

Learner Tien and Alex Michelsen were born about 15 months apart and first crossed paths a decade ago when they were playing in Southern California tennis tournaments for kids. Tien, now 19, and Michelsen,

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