Tien the youngest man into Australian Open last 16 since Nadal

American qualifier Learner Tien became the youngest man to reach the Australian Open fourth round in 20 years as he beat an ailing Corentin Moutet 7-6(10) 6-3 6-3 on Saturday, continuing the teenager's fairytale run at Melbourne Park.

Less than two months after his 19th birthday, world number 121 Tien already had the more experienced Moutet's measure before the French world number 69 was hit with trouble in his upper left leg in the late afternoon clash at Kia Arena.

Tien's win in the battle of lefthanders came two days after he pulled off the upset of the tournament by beating former US Open champion and three-times finalist Daniil Medvedev in a five-set thriller.

The Californian is the youngest man to get to the fourth round since an 18-year-old Rafa Nadal in 2005.

"It feels great, obviously," said Tien, who will face unseeded Italian Lorenzo Sonego for a place in the quarter-finals.

"This exceeded my expectations coming into this week, you expect to win every match but to be in the second week is amazing."

A number of teenagers have impressed at Melbourne Park, with Brailian Joao Fonseca and Czech Jakub Mensik also bundling out top 10 seeds.

But Tien is the last teen standing in a second week cohort dominated by veterans like 37-year-old Novak Djokovic and 38-year-old Monfils.

Among American men, only an 18-year-old Pete Sampras was younger when he reached the fourth round in Melbourne.

Tien will have young American company in the fourth round, though, with impressive 20-year-old Alex Michelsen swatting aside Russian 2023 semi-finalist Karen Khachanov 6-3 7-6(5) 6-2 in two hours and 15 minutes at John Cain Arena.

Michelsen, who upset 11th seed Stefanos Tsitsipas in the first round, became the youngest American to claim multiple top 20 victories at a Grand Slam since Sampras and Andre Agassi at the 1990 US Open.