Top-seeded Janko Tipsarevic lost in the second round of the Power Horse Cup on Wednesday, falling 7-6 (1), 6-1 to Argentine qualifier Guido Pella.
It's the biggest career win for the 101st-ranked Pella, knocking out the 10th-ranked Serb to reach the ATP World Tour quarterfinals for the first time.
Pella will play seventh-seeded Viktor Troicki of Serbia, who defeated Grega Zemlja of Slovenia 6-3, 7-6 (3).
Third-seeded Juan Monaco of Argentina topped Andre Ghem 6-4, 6-4 of Brazil to set up a quarterfinal with Tobias Kamke, who beat Aljaz Bedene 6-1, 6-4.
Second-seeded Tommy Haas of Germany rallied past Ivan Dodig 3-6, 6-4, 7-5. The German will next play Jarkko Nieminen, who defeated Roberto Bautista Agut 6-4, 5-7, 6-3.
Igor Sijsling knocked out fourth-seeded Philipp Kohlschreiber 3-6, 6-3, 6-4 and will play Jan Hajek. The Czech routed Daniel Brands 6-1, 6-0.