Estoril - Stefanos Tsitsipas swept the last seven points of the match to defeat Roberto Carballes Baena 6-7 (2/7), 6-2, 7-6 (7/3) on Friday for a place in the semi-finals of the Estoril Open.
The 19-year-old Greek, a surprise finalist last weekend in Barcelona against Rafael Nadal, will aim for his second straight title match as he takes on Portuguese number one Joao Sousa, who beat British third seed Kyle Edmund 6-3, 1-6, 6-0.
The 44th-ranked Tsitsipas recovered from 0-3 down in the final-set tiebreaker, erasing the deficit and sprinting to a victory that was sealed when his 77th-ranked opponent drove a return long.
The battle between first-time opponents lasted for nearly two and three-quarter hours.
"I was really focused after 0-3 in the tiebreaker," the youngster said. "The two points after that were important for the win.
"I had to keep the score as close as possible. After those two points, I got the upper hand.
"I was patient during the rallies. Winning seven points in a row is unbelievable. I had the momentum and I kept it to the end."
Tsitsipas is coming off his best performance on clay and just defeated his second top-10 opponent in as many weeks, adding Estoril top seed Kevin Anderson to his list of victims on Thursday.
Last week, the outsider beat world No 7 Dominic Thiem in the quarter-finals.
"After last week in Barcelona, I told myself I had to keep my level and concentration," Tsitsipas said. "That is a difficult challenge.
"At the start of the match I was frustrated, but I got tired of my attitude and stopped complaining and just played."
Sousa, who has been playing his home event since 2008, produced his best career showing at the tournament as he thrilled local fans with his victory over Edmund.
The world number 68 will be competing in his second semi-final of 2018 after reaching the last four in Marrakech a month ago.
Results at the ATP Estoril Open on Friday (x denotes seeding):
Stefanos Tsitsipas (GRE) bt Roberto Carballes Baena (ESP) 6-7 (2/7), 6-2, 7-6 (7/3)
Joao Sousa (POR) bt Kyle Edmund (GBR x3) 6-3, 1-6, 6-0
Frances Tiafoe (USA) bt Simone Bolelli (ITA) 7-5, 6-2