Blaz Kavic shocked sixth seed Marcos Baghdatis to reach the quarter-finals of the ATP Zagreb Indoors.
The Slovenian - who had not previously reached the last eight of an ATP event since July 2011 - rallied from a set down to defeat the 2007 champion 3-6 7-6 (7/2) 6-4 after two hours and eight minutes on court.
Baghdatis, who had served for the match in the second set before eventually losing it in a tie-break, immediately afterwards pulled out of the doubles because of a foot injury.
"I did not want to take any risks," he said. "I have to give credit to Kavcic, he played well."
The Cypriot was not the only seed to fall on Thursday - No.5 Martin Klizan was beaten by Robin Haase, the Dutchman triumphing 6-2 4-6 6-4 in just under two hours.
Haase will next meet Germany's Philipp Petzschner, who defeated Croatian lucky loser Dino Marcan - a replacement for the ill Andreas Seppi - 6-3 6-4.
There were few problems for top seed Marin Cilic, who defeated Grega Zemlja of Slovenia 6-3 6-2 as he looks for a third Zagreb title. Cilic will now take on Baghdatis' conqueror Kavic.
Jurgen Melzer is also through to the last eight, the fourth-seeded Austrian recovering from a disastrous opening set against Somdev Devvarman of India to win 1-6 7-6 (7/5) 6-2.
Meanwhile, Lukas Rosol - the man who famously knocked Rafael Nadal out in the second round at Wimbledon last year - ousted Italy's Flavio Cipolla 6-4 2-6 6-3.
Ivan Dodig of Croatia is also through to a meeting with defending champion Mikhail Youzhny after overcoming countryman Ivo Karlovic 7-6 6-7 6-3.