Steve Darcis upset former champion and fourth-seeded Radek Stepanek in the afternoon session of the second round of the SAP Open, 7-6 (7), 7-6 (7) on Thursday.
Stepanek of the Czech Republic is ranked 29th in the world while Darcis is ranked 72nd in the world and is 22nd-seed of the tournament.
Belgium's Darcis needed tiebreakers in both sets to defeat the 2009 SAP Open champion.
It was the first meeting between the two since 2008 when they split their two matches.
Fifth-seeded Julien Benneteau of France defeated Gilles Muller of Luxembourg, 6-2, 6-4 and will face Darcis in the quarterfinals.
Sixth-seeded Kevin Anderson of the United States and qualifier Dimitar Kutrovsky of Bulgaria also advanced to the quarterfinals.