Sebastian Korda and Lorenzo Sonego progressed to the second round of the Moselle Open on Monday, while Stanislas Wawrinka came through qualifying.
Korda was playing his first indoor match since the decider of the Next Gen ATP Finals last November, and Hugo Gaston represented a tough opening test.
But the American prevailed in straight sets against the home favourite, winning 6-3 7-6 (7-2) after defending set points in the second set and blowing his opponent away in the subsequent tie-break.
Another tricky opponent awaits, with number three seed Lorenzo Musetti up next in the second round.
Musetti’s Italian compatriot Sonego also succeeded in Monday’s only other main-draw match, beating sixth seed Aslan Karatsev 7-5 6-3 to set up a last-16 clash with either Gilles Simon or David Goffin.
In the qualifying section, three-time grand slam champion Wawrinka beat Zsombor Piros 6-7 (4-7) 6-2 6-0 to reach the first round, where Joao Sousa awaits.
The winner of that match will face top seed Daniil Medvedev in the last 16.