Carreno Busta, 26, has always been a player of some potential, but this season he has progressed by reaching the quarter-finals at the French Open in June.
Carreno Busta will face the winner of Tuesday's night match in New York between Wimbledon semi-finalist and 17th seed Sam Querrey and another big server in the 28th seeded Kevin Anderson of South Africa.
The 12th seed has gone one better at Flushing Meadows following this impressive victory over diminutive Argentine Schwartzman that leaves him as the highest seed left in the ravaged bottom half of the draw where nobody left is inside the top 10.
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He has yet to drop a set in winning five straight matches in New York at the season's final major.
The 26-year-old dropped his racket and pumped his fists in celebration, and he said: "It's incredible. It's something that I always dreamed of but never think I can arrive here.
It's very exciting to be in the semi-finals. It was a very good match today. I tried to be focused all the time, Diego is a fighter. You need to be aggressive all the time and try to dominate the points.

Highlights: Carreno Busta’s fine run continues

Schwartzman’s impressive victory over fifth seed Marin Cilic in the last 32 and 16th seed Lucas Pouille in the fourth round were shocks, but his surprise journey ended against an assured Carreno Busta, who always looked like a figure in control of his own destiny.
As he did in the first set, Carreno Busta broke in the first game of the third and although Schwartzman battled hard to stay in the set with a couple of incredible shots, he was unable to stop the Gijon man's victory march in one hour and 58 minutes.
Carreno Busta had the easier run to the quarter-finals, beating four qualifiers all in straight sets, and he almost certainly benefited from his extra freshness.
Schwartzman was playing in the last eight at a slam for the first time after upsetting Marin Cilic and Lucas Pouille.
But he struggled with a leg problem against Pouille and ultimately could not quite match the consistency of Carreno Busta.
It was a closer match than the scoreline suggested but, as in his fourth-round victory over Denis Shapovalov, Carreno Busta played the big points superbly.
The Spaniard saved eight of the 10 break points he faced while taking six of eight chances on Schwartzman's serve.
There remains the prospect of an all-Spanish final with Rafael Nadal on Sunday if the world number one can win his next two matches against Andrey Rublev and a potential semi-final with Roger Federer or Juan Martin del Potro.

Results from the US Open Men's Singles Quarterfinal matches on Tuesday

12-Pablo Carreno (Spain) beat 29-Diego Schwartzman (Argentina) 6-4 6-4 6-2
Brilliant Nadal battles past Schwartzman to reach semis
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'Amazing' Nadal shot leaves Schwartzman scratching his head
09/06/2021 AT 15:17