Learner Tien hits a return during the men's singles semifinal match between Daniil Medvedev of Russia and Learner Tien of the United States at 2025 China Open tennis tournament in Beijing, China, Sept. 30, 2025. (Xinhua/Xie Han)

American teenager Learner Tien advanced to his first ATP Tour final at the China Open on Tuesday after eighth seed Daniil Medvedev of Russia was forced to retire while limping heavily in the deciding set of their semifinal clash.

The 19-year-old Tien, ranked 52nd, prevailed 5-7, 7-5, 4-0 on Diamond Court, setting up the showdown with top seed Jannik Sinner, who booked his third consecutive final in Beijing by defeating Australia's Alex de Minaur 6-3, 4-6, 6-2 earlier in the day.

It was Tien's second career meeting with Medvedev, having stunned the 2021 US Open champion in a five-set epic at this year's Australian Open en route to the round of 16.

Tien started his match strong in the opening set, breaking twice for a 3-0 lead, but Medvedev managed to claw back before breaking in the 12th game to take the opening set 7-5.

The second set swung wildly. Medvedev moved 3-0 up with an early break, only for Tien to reel him in. After trading breaks to 5-4, Tien held serve for 5-5, then broke from deuce for 6-5 and served out the set 7-5.

Medvedev received a medical time-out after the second set. As the decider began, his movement was clearly compromised. Limping between points and struggling to push off on serve, he dropped four straight games before halting play. Shaking hands at the net, the 29-year-old hobbled off court, leaving the Beijing crowd in shock.

For Tien, the victory capped a breakthrough season that began with a sensational run from qualifying to the Australian Open fourth round.