Argentine Schwartzman was looking to book his place in the last eight in Miami for the first time, which would have been his sixth quarter-final appearance at this level, but he came unstuck against the 20-year-old American.

Korda defeated Schwartzman 6-3, 4-6, 7-5 to claim his first victory over a top-10 player.

"I played an incredible match today," said Korda.

"I think mentally I was great out there.

"I stayed calm.

"Even when in the tight situations I believed in myself and I went for it.

"I'm super proud of that.

"All the hard work that I have done with my team is paying off."

Korda was the youngest of four American men to start the day but was the last man standing by the end of it.

US number one and 2018 champion John Isner fell at the last-16 stage as Spain’s Roberto Bautista Agut saved a match point in his 6-3, 4-6, 7-6 (7-5) victory in two hours and 18 minutes.

Bautista Agut can now look forward to facing Russian top seed Daniil Medvedev who also dispatched an American.

Medvedev ended Frances Tiafoe’s run in Miami with a 6-4, 6-3 triumph.

Fourth seed Andrey Rublev of Russia saw off Croatia’s Marin Čilić 6-4, 6-4 to set up a showdown with Korda.

There was also a straight-sets victory for second seed Stefanos Tsitsipas.

The Greek fired 20 winners and did not face a break point in his 6-2, 7-6 (7-2) success over Italy’s Lorenzo Sonego.

Hubert Hurkacz will meet Tsitsipas in the quarter-finals after the Pole came through a nail-biting contest against Canadian Milos Raonic, winning 4-6, 6-3, 7-6 (7-4).

Italian Jannik Sinner reached his first ATP Masters 1000 quarter-final by beating Finland’s Emil Ruusuvuori 6-3, 6-2.

Sinner will now face Kazakhstan’s Alexander Bublik who clinched a come-from-behind 6-7 (5-7), 6-3, 6-4 win against home favourite Taylor Fritz.

In the women’s draw, defending champion and world number one Ashleigh Barty of Australia defeated seventh seed Aryna Sabalenka of Belarus 6-4, 6-7 (5-7), 6-3 to book her place in the semi-finals.

"It was a brilliant match today," said Barty.

"It was certainly the best level I’ve played for a long time and especially over a sustained period."

Barty will meet Ukrainian Elina Svitolina - who saw off unseeded Latvian Anastasija Sevastova 6-3, 6-2 - next.

The Women's Tennis Association 1000 and ATP Masters 1000 tournament continues tomorrow.