Basel - Stefanos Tsitsipas reached his 13th quarter-final of 2019 on Thursday when he came back to claim a 6-7 (4/7), 6-2, 6-4 win over Lithuanian qualifier Ricardas Berankis at the ATP Swiss Indoors.
The Greek third seed will next face Italian fifth seed Fabio Fognini or Filip Krajinovic of Serbia for a semi-final spot.
Tsitsipas said he didn't panic after losing the opening set to his 70th-ranked opponent in 52 minutes.
"He was giving me a hard time in the first set, it was not easy to overcome, we had a high-quality match," said Tsitsipas, the world number seven.
"I managed to remain calm and not rush too much," the number seven said after reaching his 13th quarter-final of 2019.
"I knew things would work out, I was able to break twice in the second set and once more in the third. I was serving well and that took some of the extra pressure away.
"Sometimes it's tough to manage the energy. But getting angry sometimes can actually help. It can give you an extra reason to fight."
The ATP Finals' hopes of David Goffin stalled as the sixth seed lost to Reilly Opelka 6-7 (4/7), 7-6 (7/4), 7-5, with the young American sending down 29 aces in two and a half hours.
Goffin stands provisional tenth in the race to the eight-man season wrap-up with a final points-earning chance next week at the Paris Masters.
Rafael Nadal, Novak Djokovic, Roger Federer, Daniil Medvedev, Dominic Thiem and Tsitsipas have already booked their places in the ATP Finals, leaving just two places available.
Roberto Bautista Agut, who sits one spot away from a London invitation, stayed in the chase as he defeated France's Richard Gasquet 6-2, 4-6, 6-3 and will next play Opelka.
The Spaniard claimed his 40th victory of the season as he works to become a first-time qualifier into the season showpiece in London which starts on November 10.
Results from the ATP tournament in Basel on Thursday (x denotes seeding):
Stan Wawrinka (SUI x7) bt Frances Tiafoe (USA) 6-3, 3-6, 7-5
Stefanos Tsitsipas (GRE x3) bt Ricardas Berankis (LTU) 6-7 (4/7), 6-2, 6-4
Reilly Opelka (USA) bt David Goffin (BEL x6) 6-7 (4/7), 7-6 (7/4), 7-5
Roberto Bautista Agut (ESP x4) bt Richard Gasquet (FRA) 6-2, 4-6, 6-3