John Millman has beaten German Jan-Lennard Struff in straight sets at the German Open to set up a tricky second round clash with world No.8 Dominic Thiem.
The Australian saved three break points to overcome Struff 7-5 6-3 in one hour and 31 minutes on clay at Hamburg's Am Rothenbaum.
Meanwhile, Thiem marked his return from an injury layoff with a 6-4 6-2 victory over qualifier Corentin Moutet.
The French open runner-up's Wimbledon adventure was cut short earlier this month after he was forced to retire with a back injury in his opening round match against Marcos Baghdatis.
Chasing his third hard court title of the season, the Austrian looked in fine form against Moutet as he claimed a decisive break in the seventh game to win the opening set.
Frenchman Moutet, ranked 119th in the world, threatened a comeback when he secured an early break in the second set but Thiem reeled off six consecutive games to seal victory.
Third-seeded Spaniard Pablo Carreno Busta edged wildcard Florian Mayer 2-6 6-1 7-6 (7-4) while seventh-seeded Frenchman Richard Gasquet overcame countryman Benoit Paire 7-5 6-3.
Nikoloz Basilashvili upset German fifth seed Philipp Kohlschreiber 7-5 1-6 6-4 while eighth-seeded Spaniard Fernando Verdasco progressed with a 6-3 4-6 7-6 (7-5) win over Dusan Lajovic.
Gael Monfils moved into the second round with hard-earned 6-4 3-6 6-4 win over Italian sixth seed Marco Cecchinato.
The 31-year-old Frenchman put 95 per cent of first serves into court and converted three of his five break-point chances to secure victory.
"I was very good in my movement, but also my serve," Monfils said.
"I like to serve with a little bit less speed, [reach] his backhand and try to control the court with my forehand, so I was happy with that."
Monfils will next meet defending champion Leonardo Mayer.
The other first-round winners on Tuesday were Pablo Cuevas, Aljaz Bedene and Thiago Monteiro.