German Mischa Zverev cruised past top seed and world number seven Gilles Simon 6-4 6-2 to advance to the quarter finals of of the Stuttgart tournament.
Simon, still in search of his first tournament win of the season, had no answer to the left-hander's versatile game on clay.
Zverev, was also beaten the Frenchman in Rome earlier this year in their only previous encounter.
Simon was the second seeded player to tumble. Fifth-seed Philipp Kohlschreiber slumped to a surprise 6-2 6-4 defeat against Polish qualifier Lukasz Kubot.
The 127th-ranked Pole grabbed a break in the first game and added another in the seventh to clinch the first set before breaking the world number 26 again early in the second to serve out the match after 70 minutes.
Second seed, Russian Nikolay Davydenko, the world number 11, had little trouble against German Michael Berrer, ranked 109 places lower, sweeping past him 6-3 6-3 after only 66 minutes.
He will now meet 22-year-old Italian Fabio Fognini who advanced after Paul-Henri Mathieu, trailing 6-4 4-1, retired with an injury.
