Towering Croat Ivo Karlovic toppled third seed Novak Djokovic 7-6, 7-6 to make the quarter-finals of the Madrid Masters on Thursday.
The 14th seed will meet Frenchman Gilles Simon next after unsettling Djokovic with his booming serves.
Both sets went to tiebreaks, which favoured Karlovic, who blasted 20 aces, to Djokovic's eight.
Earlier, world number one Rafael Nadal, Roger Federer and Andy Murray all made it to the last eight, but defending champion David Nalbandian went out.
Federer comfortably beat Jo-Wilfried Tsonga 6-4, 6-1, taking the first when Tsonga double-faulted on his serve.
"It got easier for me as the match went on. It is the first time I have played him and I had expected it to be much harder," said Federer.
In the only quarter-final contest featuring two seeds, he will face Argentina's Juan Martin del Potro.
The ninth seed beat compatriot and seventh seed Nalbandian 6-4, 6-2 in just 85 minutes.
"He played very well, was very solid. I started both sets badly. He took advantage and maintained it throughout the match," Nalbandian said of his Davis Cup team mate.
Top seed Nadal booked his place by breezing past an out-of-sorts Richard Gasquet 6-4, 6-2.
It was a much more convincing performance from the top seed, who had laboured through his opener against Ernests Gulbis on Tuesday, and he showed little sign of suffering from the muscle strain that forced him out of the doubles as a precaution.
"I am much better. I spent the afternoon with the physio yesterday and we'll have to see how it goes," said the Spaniard.
"[Against 15th seed Gasquet] I was much better than on my first day and he committed more errors than usual, particularly on his backhand."
Next for up for Nadal is compatriot Feliciano Lopez, who saw off Switzerland's Stanislas Wawrinka 6-4, 6-4.
Fourth seed Murray was forced to work for it against big-serving Croatian Marin Cilic 7-5, 7-6. He faces France's Gael Monfils who put out the eighth seed Andy Roddick 6-4, 3-6, 6-3. Murray was broken early and was staring down the barrel in the ninth game of the opening set as 20-year-old Cilic held three set points.
But the Scot roared back thanks to some stinging returns, including one right into the feet of the lofty Croatian, to break back. He then broke again to take the set.
Despite suffering from a sore knee, Murray served for the match at 5-3 in the second but Cilic broke back and took it to the tiebreak which the Scot won 7-2.
"I hit some great shots to break him. Once I got my chance I took it," he said.