Swiss youngster Dominic Stryker stunned second seed Hubert Hurkacz 7-6 (5) 7-6 (5) on Thursday to reach the quarter-finals of the Stuttgart Open.
The 18-year-old, seeded 335, showed his composure again in the tiebreak a day after beating Radu Albot 7-6 (4), 7-6 (5) in his first grasscourt debut.
Striker hit eight aces and saved five of his six break points against Hurkacz to set up a meeting with Sam Querrey. He defeated American qualifier James Duckworth 6-4, 7-6 (7).
Stryker was ranked #1168 at the start of the season but is climbing fast. He also reached the quarter-finals of his first major draw on the ATP Tour in Geneva three weeks ago.
Third seed Felix Auger-Aliassime beat South African Lloyd Harris 6-3, 7-6 (4). The Canadian will then play the sixth seed Ugo Humbert, who beat favorite at home Yannick Hanfmann 7-6 (9), 6-2.
Fourth seed Alex de Minaur also won an all-Australian match against Jordan Thompson 6-7 (8), 6-3, 6-4 in the quarter-final against Austrian Jorg Rodionov.
Rodionov, ranked 142nd, was up 5-3 when German Peter Gojowczyk was forced to retire.
Marin Cilic beat Nikoloz Basilashvili 6-3 6-2 and was waiting for a win between Denis Shapovalov and Feliciano Lopez.