Daniil Medvedev on Wednesday got his revenge against US teenager Learner Tien, beating him in a nail-biter 7-6 (8/6), 6-7 (1/7), 6-4 to proceed to the Shanghai Masters quarter-finals.

There he will meet world number seven Alex de Minaur, who cruised past Portugal's Nuno Borges 7-5, 6-2 earlier in the day.

Victory in Shanghai comes just over a week after the 36th-ranked Tien took the Russian out of the China Open semi-finals in Beijing.

"He's an unbelievable tennis player," Medvedev said of the 19-year-old. "Outside of the big three, he may be the toughest opponent I've ever faced."

Medvedev broke first in the ninth game, but Tien returned the favour immediately.

The last two games of the first set saw the two players locked in an epic back-and-forth, their prolonged rallies thrilling the crowd.

Both faced breakpoint but managed to hold, with Medvedev smashing a looping lob from Tien to send them to a gripping tiebreak.

Medvedev broke early in the second set, but Tien was again unphased –- breaking back in the fifth and then seventh games, before the former world number one levelled in the tenth.

Medvedev began limping just before the second-set tiebreak and spoke briefly with a medic before hobbling back onto court.

Tien went 3-0 up as the Russian, ten years his senior, tried to stretch out on court, becoming increasingly irate as the match was pushed to a decider.

"I should be more calm, but Learner drives me nuts... I lost two very traumatic matches against him -- so for sure I was scared to lose again," he said.

But a scrappy third set -- full of double-faults from both players -- was settled when Medvedev broke in the ninth game with a backhand.

- 'Going to be a battle' -

The Russian said he would need to rest his legs in anticipation of a similarly tough challenge against De Minaur on Friday, smiling wryly: "We're gonna run again".

After Novak Djokovic, the Australian is the highest ranked player left standing after a string of high-profile exits.

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Australia's Alex de Minaur celebrates after beating Portugal's Nuno Borges / © AFP

De Minaur needed five break points in the 11th game against Borges in the first set, converting the last with a backhand for a decisive advantage.

He carried the momentum into the second set, breaking in the first and third games.

But he remained cautious about his title chances.

"In our side of the draw, there's a lot of quality players, so it's still going to be a battle," he said.

Another top-10 player fell on Wednesday as Italy's Lorenzo Musetti lost to Canada's Felix Auger-Aliassime 6-4, 6-2.

Thirteenth-ranked Auger-Aliassime looked sharp throughout, breaking in the fifth game.

He went on to dominate the second set, breaking Musetti, the world number nine, in the fifth and seventh games.

"I knew it was going to be the toughest match of the week so far, and I knew I was going to have to raise my level, and I did," said the 25-year-old Canadian.

He will next meet France's Arthur Rinderknech, who reached his first Masters 1000 quarter-final after beating Czech Jiri Lehecka 6-3, 7-6 (7/5).

Rinderknech's cousin Valentin Vacherot made it to the last eight on Tuesday, and will face Denmark's Holger Rune for a place in the semi-finals.

Djokovic will follow them on to court on Thursday against Belgium's Zizou Bergs for a place in the last four.