Rafa Nadal suffered his first clay court defeat in 23 matches on Thursday and threatened to boycott next year's Madrid Open if officials did not ditch the blue clay that players have labelled "too slippery" and only fit for "smurfs (to) play on".
After a shock 6-3 3-6 7-5 third-round reverse to fellow Spaniard Fernando Verdasco, the French Open champion vowed not to return to the Masters event unless traditional red courts, which are slower and more suited to his game, were reinstated.
"The movements are very important for me and here I cannot move so I cannot hit the ball the way that I want," he told a news conference after squandering a 5-2 lead in the final set.
"The ATP and the tournament can do what they want," he added referring to the controversial innovation sanctioned by the governing body of men's tennis for this year's tournament.
"I tried my best to prepare but I wasn't good enough to adapt my game to this court.
"The only thing that I know is that if things continue like this I am very sad but next year will be one less tournament in my calendar."
Nadal's outburst was perhaps understandable considering he would have fancied his chances of beating Verdasco, the 15th seed, having won all 13 of their previous meetings.
However, an error-strewn performance ended the world number two's bid for a third straight clay title this season and deprived him of a chance to avenge his defeat by Novak Djokovic in last year's final.
Roger Federer, the world number three and 2009 champion, cruised into the last eight with a 6-3 6-2 win against French 14th seed Richard Gasquet and will meet fifth-seeded Spaniard David Ferrer for a place in Saturday's semi-finals.
The Swiss maestro had a tough time in the second round on Wednesday, edging out big-serving Canadian Milos Raonic, but had no such trouble against Gasquet as he chases a fourth title of the year.
Verdasco's first win against Nadal was all the more astonishing given that Nadal twice failed to serve out the match in the deciding set.
Verdasco broke his Davis Cup team mate seven times in all, losing his own serve six times, and clubbed 31 winners to his opponent's 19. A typically crashing forehand drive sealed victory on his second match point and he fell flat on his back on the court before kissing the clay and heading off to play a doubles match.
"I lost because I deserved to lose today," Nadal said.
"Even when I was 5-2 ahead and I had a chance to close the match I didn't know how to do it. He played better than me and he beat me, that's it."
|Serena Williams overcame a slow start to beat former number one Caroline Wozniacki [EPA]
Verdasco next plays Czech sixth seed Tomas Berdych, who was the first player into the last eight when he thrashed 12th-seeded Frenchman Gael Monfils 6-1 6-1.
He was joined by Ukraine's Alexandr Dolgopolov, the 16th seed, who edged out French fourth seed Jo-Wilfried Tsonga 7-5 3-6 7-6 and Ferrer, who squeaked past countryman Nicolas Almagro 7-6 3-6 7-6.
Dolgopolov will play 10th seed and former US Open champion Juan Martin Del Potro for a place in Saturday's semi-finals after the rangy Argentine thumped fellow big-server Marin Cilic of Croatia 6-2 6-4.
Djokovic beat unseeded Swiss Stanislas Wawrinka 7-6, 6-4 later on Thursday, setting up a meeting with the winner of the match between Gilles Simon of France, the ninth seed, and Serbian compatriot Janko Tipsarevic.
Serena Williams overcame a lethargic start to upset fellow former world number one Caroline Wozniacki and set up a quarter-final meeting with old foe Maria Sharapova.
The ninth seed powered to a 1-6 6-3 6-2 victory over the Dane, clubbing a blistering 43 winners to reach the last eight in the Spanish capital for the first time.
The winner between Williams and Sharapova will meet either fifth seed Samantha Stosur or Czech qualifier Lucie Hradecka in the semi-finals.
The 26-year-old Hradecka, who stunned third seed Petra Kvitova in the second round, beat Russia's Ekaterina Makarova 6-2 7-6 to reach the last eight.
Fourth-seeded Pole Agnieszka Radwanska, who climbed to world number three this week, won 7-6 6-4 against Italy's Roberta Vinci and will meet American qualifier Varvara Lepchenko, a 6-1 6-7 6-3 victor over Spain's Anabel Medina Garrigues.