Sebastian Korda dispatched teen wonder Carlos Alcarez from the Monte Carlo Masters on Wednesday following a gripping three-hour slugfest.
Korda, 21, won 7-6, 6-7, 6-3 to advance to the last 16.
The world number 42 went into the second round tie as the distinct underdog.
Alcaraz had won their previous meeting - the final of the NextGen tournament in 2021 - and the18-year-old Spaniard had just claimed one of the most prestigious titles on the tour at the Miami Masters to rise to 11 in the world.
But Korda was undeterred against the eighth seed. But after leading 4-2, he lost three consecutive games to give Alcaraz the chance to serve for the first set at 5-4.
However, Alcaraz was in generous mood and let Korda back in at 5-5. The unseeded American exploited his good fortune to take the tiebreak seven points to two.
After levelling the match courtesy of a tiebreak, first blood in the decider went to Alcaraz but Korda reeled him in for 2-2.
Battle
It was level pegging until Alcaraz had the chance to square proceedings at 4-4.
He faltered and gave Korda the chance to serve for the match.
He squandered his first match point thrashing a forehand long with the court gaping.
But on his second match point, Alcaraz was unable to steer a powerful serve back into the court.
"He beat me in the final of the Next Gen Masters last year so it is great to take my revenge," said Korda.
"Carlos is an extraordinary player with a great future ahead of him," he added.
Before the tournament, the talk was about a possible last eight showdown between the top seed Novak Djokovic and Alcaraz.
But Djokovic was eliminated on Tuesday and Alcaraz has followed him out of the first major clay court tournament of the season.
