Fifth seed Daniil Medvedev is out of the Australian Open after losing a five-set thriller to teenager Learner Tien in the biggest upset of the tournament so far.

Medvedev, a three-time finalist in Melbourne, saved match point in the third set and forced a decider, but ultimately fell to a 6-3 7-6 (7-4) 6-7 (8-10) 1-6 7-6 (10-7) defeat by the 19-year-old qualifier.

American Tien, ranked 121st in the world, celebrated in front of a largely empty Margaret Court Arena after wrapping up the win at 02:54 local time in Melbourne.

“I was definitely hoping it wasn’t going to a fifth-set breaker but either way I’m just really happy to get the win,” Tien said after four hours and 49 minutes on court.

“I know I made it a lot harder than what it could have been but, you know, whatever.”

Before this week’s tournament Tien had never won a Grand Slam match, losing in the first round in all three of his US Open appearances.

Medvedev, who lost to Jannik Sinner in last year’s final, seemed like the clear favourite to win the match after steamrolling his way through the fourth set in 27 minutes, with Tien looking fatigued.

But, after a brief rain delay, the left-handed Californian dug deep to break back in the decider and force a 10-point tie-break.

“Losing the third [set] was tough after playing for that long. I had a match point so that was a little disappointing to see a fourth [set],” Tien said.

“In the fourth set I just had to pee so bad, so I was trying to finish it up fairly quick.

“I also wanted to start the fifth [set] serving first so I scrapped out that game at 0-5 and it all worked out.”

He is the third teenager this week, after Joao Fonseca and Jakub Mensik, to have beaten a top-10 player.

Fonseca stole the headlines with his first-round win over ninth seed Andrey Rublev, but it is Tien, who finished runner-up to the Brazilian in December’s Next Gen ATP Finals, that has gone further of the two in Melbourne.

Tien will face France’s Corentin Moutet, ranked 69th, in the third round.