Felix Auger-Aliassime and Milos Raonic both recorded notable wins at the Stuttgart Open on Tuesday but Denis Shapovalov failed to join his fellow Canadians in the second round.
Teenager Auger-Aliassime impressed in his first ATP Tour outing on grass, beating Ernests Gulbis 7-5 6-3 to set up a clash with Frenchman Gilles Simon, who fought back from a set down against Peter Gojowczyk.
Last year's runner-up Raonic, meanwhile, was made to work in his return from a knee injury, eventually overcoming qualifier Alexei Popyrin 6-7 (6-8) 6-4 7-6 (7-4) in his first competitive outing since March.
However, compatriot Shapovalov was a surprise early casualty at the tournament, the eighth seed losing to German Jan-Lennard Struff for the third time in as many months.
Meanwhile, fifth seed Gael Monfils came through a tense tie-break in the final set to see off Steve Johnson. The 2010 finalist will next face American Denis Kudla.
At the Rosmalen Grass Court Championships in 's-Hertogenbosch, David Goffin and Richard Gasquet enjoyed contrasting victories.
Belgian fifth seed Goffin had few problems against Spanish qualifier Alejandro Davidovich Fokina, easing to a 6-0 6-2 triumph after just 48 minutes on court.
Eighth seed Gasquet needed two hours and 26 minutes to see off Aljaz Bedene, the Frenchman rallying from a set down to go through 6-7 (3-7) 7-6 (7-5) 6-4.