Spanish 17-year-old Carlos Alcaraz reached the Andalucia Open semi-finals on Friday and will now attempt to become the ATP's youngest finalist since Rafael Nadal in 2004.
Alcaraz, ranked 133 in the world, brushed aside Norwegian third seed Casper Ruud 6-2, 6-4 and will face compatriot Jaume Munar on Saturday for a place in the final.
Nadal was also 17 when he was runner-up in Auckland in 2004.
Australia's Lleyton Hewitt was just 16 when he claimed the 1998 Adelaide title.
Saturday's other semi-final on the clay courts of Marbella will feature top seed Pablo Carreno-Busta against Albert Ramos Vinolas.
That means a semi-final line-up featuring four players from the same country for the first time since Valencia 17 years ago when once again Spain monopolised the places.
Results from the ATP tournament in Marbella on Friday (x denotes seeding):
Pablo Carreno-Busta (ESP x1) bt Kwon Soonwoo (KOR x7) 6-4, 6-0
Albert Ramos Vinolas (ESP x4) bt Norbert Gombos (SVK) 6-7 (4/7), 7-5, 6-4
Carlos Alcaraz (ESP) bt Casper Ruud (NOR x3) 6-2, 6-4
Jaume Munar (ESP) bt Ilya Ivashka (BLR) 6-7 (5/7), 6-4, 6-4