Qualifier and 19-year-old Learner Tien beat No. 5-ranked and three-time Australian Open finalist Daniil Medvedev in a five-set thriller 6-3, 7-6 (4), 6-7 (8), 1-6, 7-6 (7) for the biggest win of his young career.

After capturing a two-set lead, Tien appeared to be slipping when Medvedev mounted a rally to tie it and take it to the decisive fifth set. However the teen stayed composed and secured match point off a return from Medvedev that went out of bounds, capping off the major victory in a nearly-five hour match as the clock nearly hit 3 a.m. in Melbourne.

“I’m just really happy to get a win. I know I made it a lot harder than maybe it could have been, but whatever,” Tien said in his on-court interview after the victory.

With the win, Tien became the second-youngest American man to reach the third round at the Australian Open after Pete Sampras did it in 1990 at 18 years old.