Dominic Thiem upset the eight-seeded Marcel Granollers 2-6, 6-3, 7-5 in the Hamburg Open second round on Tuesday.
The 55th-ranked Austrian saved five of the eight break points he faced and converted three of his 12 chances to defeat the Spaniard in 2 1/2 hours. Granollers, ranked 40 places above Thiem, was granted a first-round bye at the clay-court event.
Thiem awaits either Guillermo Garcia-Lopez of Spain or Leonardo Mayer of Argentina, who defeated German wild card Peter Gojowczyk 6-3, 6-2.
Also in the first round, 2012 champion Juan Monaco defeated Pere Riba of Spain 6-3, 6-1. The Argentine next faces Andreas Seppi of Italy.
Poland's Jerzy Janowicz defeated Spanish qualifier Albert Ramos-Vinolas 6-0, 7-5 for a second-round clash with the fourth-seeded Alexandr Dolgopolov of Ukraine.