Stefanos Tsitsipas needed to see off a tough opening-set challenge before beating qualifier Pablo Cuevas 7-5, 6-4 on Thursday to reach the quarter-finals of the ATP tournament in Hamburg.
Tsitsipas, the top seed in Hamburg after US Open semi-finalist Daniil Medvedev was knocked out in the first round, saved four break points at 4-4 and another at 5-5 in the first set.
The 22-year-old then pulled away to take the first set and then clinch his 20th match win this season.
In the quarter-finals, Greek Tsitsipas, who is ranked sixth in the world, will face Serbia's Dusan Lajovic.
Lajovic, 30, needed just over an hour to blast his way into the last eight with a 6-1, 6-2 win over Russian eighth-seed Karen Khachanov.