Rudolf Molleker claimed his first ATP Tour win on Monday as he stunned Jan-Lennard Struff at the Stuttgart Open.
The 17-year-old sent down 26 aces to defeat his German compatriot 6-4 6-7 (5-7) 6-3 in only his second tour-level main draw match.
Molleker, who will now face Lucas Pouille in the second round, said: "It's an unbelievable feeling to earn my first main draw win on home soil. It felt great to have the crowd have my back and I just enjoyed the centre court feeling. It's a great experience for me and hopefully I can go on."
The other first-round matches saw Mischa Zverev beat Mikhail Youzhny 7-6 (7-5) 6-3, Florian Mayer claim a 6-4 6-1 win over Yannick Maden and Guido Pella ease past John Millman 6-2 6-2.
Meanwhile at the Rosmlaen Grass Court Championships, there were 39 aces as sixth seed Robin Haase came through a tough opening test against Ivo Karlovic, winning 7-6 (7-3) 6-7 (5-7) 6-3.
Seventh seed Yuichi Sugita had an easier time of things, beating Nikoloz Basilashvili 6-3 6-2, and there were also victories for Daniil Medvedev and Marius Copil.