US Open semi-finalist Ben Shelton fought back from a set down to defeat Jannik Sinner on Tuesday and reach the Shanghai Masters last eight in one of the biggest victories of his young career.
The 19th seed emerged from an excruciatingly tight deciding set to battle through 2-6, 6-3, 7-6 (7/5) and will face fellow American Sebastian Korda in the quarter-finals.
Shelton, who lost to Novak Djokovic in the last four in New York last month, did his now-trademark "dialled-in" celebration to mark his first time into the quarter-finals of a Masters.
The 26th-seeded Korda fended off a late fightback from the 20th seed Francisco Cerundolo of Argentina to go through 7-5, 7-6 (8/6).
Shelton, who turned 21 on Monday, endured a torrid opening set against the in-form sixth seed Sinner, summed up by his double fault to concede the seventh game of an error-strewn first stanza.
The Italian Sinner, fresh from winning the China Open in Beijing, clinched the opening set with a well-placed smash.
The athletic Shelton was a changed man in the second, sealing the set with an ace and a roar, and then immediately put Sinner under the cosh to start the decider.
The 22-year-old Sinner survived the initial onslaught, saving five break points to seal a game that lasted nearly 10 minutes, and the set went with serve to force a tiebreak.
But it was Shelton who prevailed -- and a crowd that had been on his side serenaded him by singing happy birthday.
A tournament full of shocks had another to start the day when 91st-ranked Fabian Marozsan had a belated birthday present of his own by beating eighth-seeded Casper Ruud.
The unseeded Hungarian won 7-6 (7/3), 3-6, 6-4 and will face Poland's 16th-seeded Hubert Hurkacz or home player Zhang Zhizhen in the last eight.
Marozsan sealed the deal in two hours and 38 minutes with a stinging forehand down the line on his second match point and called his maiden Masters quarter-final the perfect present, having turned 24 on Sunday.
"This is just only my second Masters tournament, so it's kind of a new tournament series for me," said the Hungarian, who beat Carlos Alcaraz at the Italian Open in May.
"I'm really enjoying this, I'm very proud for this one," added Marozsan, who is playing in Asia for the first time.
The Shanghai event, which is back on the ATP calendar for the first time since the Covid pandemic, has witnessed several shocks.
Korda dumped out second-seeded Daniil Medvedev on Sunday and the next day Stefanos Tsitsipas, the fourth seed from Greece, lost to France's 32nd seed Ugo Humbert in a three-set battle stretching beyond midnight.
The upsets have paved the way for top seed Alcaraz, who faces 18th seed Grigor Dimitrov in the last 16 on Wednesday.
World number Djokovic is not in China.