Tien thrashes Medvedev after nosebleed to make maiden Slam quarter-final
The 20-year-old American, who capped a breakout 2025 by winning the ATP Next Gen title, crushed the Russian 6-4, 6-0, 6-3 in just 1hr 42 mins on Margaret Court Arena.
It put 25th seed Tien into a last-eight clash with third-seeded German Alexander Zverev.
He is the youngest men's singles quarter-finalist at Melbourne Park since Nick Kyrgios in 2015 and the youngest American man to reach the last eight at a Slam since Andy Roddick in 2002 at the US Open.
"It feels amazing. I mean, so special to do it, especially here," Tien, who won his first career title in Metz in November, said of making his maiden quarter-final.
"It's always so special for me to come back and play here.
"Every year since I've been coming here, the crowd support has been amazing. I don't know why, honestly, a crowd like this with this much energy and support, it means the world to me to do it here."
Defeat was a sorry end for former world number one Medvedev, who was also knocked out last year by then-teenage qualifier Tien, in a five-set marathon.
This time the 11th seed Medvedev, who reached three of the last five finals in Melbourne, was a shadow of his former self.
Tien broke immediately to signal his intent, but his momentum was interrupted when he needed treatment for a nosebleed.
They resumed after a seven-minute break, with Tien taking the set.
After that it was all the American, who reeled off 10 straight games as Medvedev imploded, cutting a dejected figure.
He suddenly woke up and against the run of play won three games to give himself a glimmer of hope, before Tien seized back control and sprinted to the finish.
Medvedev was outplayed by Novak Djokovic in the 2021 final before a heart-wrenching defeat to Rafael Nadal a year later.
He lost to Jannik Sinner in 2024, crashing in five sets after being two up.