German wild card Daniel Brands stunned top seed Gilles Simon of France, beating the world number seven 3-6, 6-4, 6-3 to advance to the third round of the German Open in Hamburg on Tuesday.
The pair traded early breaks before Simon, still in search of his season's first title, broke again to race into the lead 5-2 and serve out the set two games later.
Simon got another early break to go 2-1 up in the second but the determined 22-year-old Brands, ranked 120th in the world, broke twice to lead 4-2.
The Frenchman raced back to 4-4 with some well-placed groundstrokes but Brands hung in to break again and level the match.
The German then got the break he wanted in the fifth game of the third set to go 4-2 up and serve out the match on his third match point.
World number 16 Tommy Robredo, seeded fourth, also suffered an early exit at the hands of Spanish compatriot Ivan Navarro, ranked 103rd, losing 7-5, 7-6.
Uruguayan Pablo Cuevas came from a break down in the first set to sweep past ninth-seed Juergen Melzer from Austria 7-6 6-3 while Swiss Stanislas Wawrinka, seeded fifth, lost 6-2, 6-4 to Spaniard Guillermo Garcia-Lopez.
French 13th-seed Paul-Henri Mathieu was lucky to escape against 145th-ranked Pere Riba of Spain, battling his way through three sets to win 6-1, 2-6, 7-6.
Serb Viktor Troicki, seeded 10th, also had to battle hard -- for two hours and 40 minutes -- until breaking the resistance of Russian Teimuraz Gabashvilli 3-6, 6-2, 6-4.