Estoril - Frances Tiafoe of the United States upset defending champion Pablo Carreno Busta 6-2, 6-3 to reach the Estoril Open final on Saturday.
The 20-year-old Tiafoe will face local favourite Joao Sousa in Sunday's final after the Portuguese beat Stefanos Tsitsipas 6-4, 1-6, 7-6 (7/4).
Tiafoe converted four of seven break chances to beat the second-seeded Carreno Busta on the outdoor clay court.
Tiafoe won his first ATP Tour title at Delray Beach in February.
The 19-year-old Tsitsipas committed five double faults, to go with four aces, in the loss to Sousa.
Sousa will be seeking his third career title and his first since 2015.
Results at the ATP Estoril Open on Saturday (x denotes seeding):
Joao Sousa (POR) bt Stefanos Tsitsipas (GRE) 6-4, 1-6, 7-6 (7/4)
Frances Tiafoe (USA) bt Pablo Carreno Busta (ESP x2) 6-2, 6-3