Basel - Stefanos Tsitsipas carried over the momentum from his maiden ATP title at the weekend to reach the second round of the Swiss Indoors on Wednesday with a 6-2, 7-6 (7/3) win over Jeremy Chardy.
Tsitsipas, the first Greek to lift an ATP trophy when he beat Ernests Gulbis in Stockholm on Sunday, earned his 40th victory of the season by seeing off longtime training partner Chardy.
"It was a good win for me today, I'm happy with my performance," said Tsitsipas, the world number 16.
"It was tough to come back after winning a title last week. But I'm excited about what's to come in my tennis."
Tsitsipas took revenge over Chardy for a loss to the Frenchman in Montpellier in February.
The 20-year-old had accumulated only four career tour-level match victories coming into 2018, but has enjoyed a breakthrough season and will take on Germany's Peter Gojowczyk next in Basel.
Latvia's Gulbis received on-court treatment around his hip muscle area on the way to a 7-5, 6-4 victory over fifth seed Jack Sock.
The defeat dropped the American's record this year to a dreadful 7-20 as he lost for the sixth time in his last seven matches.
Spanish eighth seed Roberto Bautista Agut defeated Portugal's Joao Sousa 6-4, 6-3, while Serbian lucky loser Dusan Lajovic beat Adrian Mannarino of France 6-7 (4/7), 6-1, 6-2.
Results from the Swiss Indoors ATP tournament in Basel on Wednesday (x denotes seeding):
Taylor Fritz (USA) bt Henri Laaksonen (SUI) 6-2, 7-5
Marius Copil (ROU) bt Marin Cilic (CRO x3) 7-5, 7-6 (7/2)
Ernests Gulbis (LAT) bt Jack Sock (USA x5) 7-5, 6-4
Roberto Bautista Agut (ESP x8) bt Joao Sousa (POR) 6-4, 6-3
Dusan Lajovic (SRB) bt Adrian Mannarino (FRA) 6-7 (4/7), 6-1, 6-2
Alexander Zverev (GER x2) bt Robin Haase (NED) 6-4, 7-5
Stefanos Tsitsipas (GRE x4) bt Jeremy Chardy (FRA) 6-2, 7-6 (7/3)