American qualifier Tien stuns Medvedev in late night epic

American teenager Learner Tien outlasted three-times Australian Open runner-up Daniil Medvedev to reach the third round with a 6-3 7-6(4) 6-7(8) 1-6 7-6(7) victory in a late-night epic on Thursday.

Qualifier Tien seemed to be fading after fifth seed Medvedev saved a match point with an ace in the third set tiebreak and stormed back from two sets down to set up a decider on Margaret Court Arena.

But the 19-year-old tapped into his last reserves of energy to become the youngest American man to reach the third round at the Australian Open since Pete Sampras did so aged 18 in 1990.

Medvedev looked clear favourite in the decider with Tien clearly fatigued but the world number 121 courageously stayed with the Russian in a series of gruelling rallies.

After a brief rain delay and with the clock approaching 3:00 am, Medvedev served for the match at 6-5 but Tien refused to go away and broke back to send the contest into a first-to-10 deciding tiebreak.

Medvedev led 6-4 but Tien stormed back to claim a sensational victory on his first match point as a weary Medvedev floated a return over the baseline to bring the near five-hour tussle to an end.