The 17-year-old Alexander Zverev reached the semifinals of his hometown tournament by defeating Tobias Kamke 0-6, 7-5, 6-3 in the Hamburg Open on Friday.
Zverev earned just six points in the opening set, but he saved seven of 11 break points and converted four chances to beat his fellow Hamburg resident in two hours.
The 285th-ranked Zverev is the first 17-year-old to reach an ATP semifinals since 2006, when Marin Cilic lost to Feliciano Lopez at Gstaad.
Zverev, who has beaten Robin Haase, No. 5 seed Mikhail Youzhny and No. 11 Santiago Giraldo, awaits either top seed David Ferrer or Pablo Andujar.
Argentina's Leonardo Mayer defeated Serbia's Dusan Lajovic 6-1, 7-5 for a semifinal with Philipp Kohlschreiber or Lukas Rosol.