Top seeds Tommy Robredo and Guillermo Coria's lack of expertise on grass was ruthlessly exposed on Wednesday when they were beaten in the second round of the Ordina Open.
Spaniard Robredo lost 6-2, 7-6 to German Lars Burgsmueller, ranked 101st in the world, while last year's runner-up and second seed Coria fell 6-3, 6-4 to unheralded Czech Jan Hernych, the world number 77.
Robredo struggled to cope with the pace of the court and Burgsmueller held his nerve to reach his first quarter-final since September 2004.
Burgsmueller came into the event having lost in the first round of his last six top-level tournaments but he belied his lack of form by romping through the first set.
Robredo looked set to hit back when he broke for 4-3 in the second but the French Open quarter-finalist dropped his own serve immediately.
The players went into a tiebreak and the German clinched it 7-5 to secure a meeting with defending champion Michael Llodra, who beat eighth seed and fellow Frenchman Paul-Henri Mathieu 6-4, 4-6, 6-3 in fading light.
"It was hard to play today with the court playing so fast," Robredo said. "But he was the better player today and I had a lot of chances but could not take them."
FULL ADVANTAGE
Second seed Coria looked out of his element in the breezy conditions of the late afternoon and Hernych took full advantage to claim the best win of his career.
"I have to say that my level of play was pretty poor today," the Argentine said. "I really have to improve my game and I have to improve on this surface."
In the women's event, second seed Nadia Petrova opened her grasscourt season with a comfortable 6-3, 6-4 win over Mariana Diaz Oliva of Argentina to reach the quarter-finals.
The Russian, seeking her first WTA Tour title, started well and after taking the opening set she broke in the seventh game of the second before sealing victory in just under an hour.
In her first appearance since reaching the French Open semi-finals, Petrova looked comfortable on the grass and Diaz Oliva struggled to cope with her power.
Petrova, the highest-ranked player left in the tournament after the withdrawal through injury of top seed Elena Dementieva, next plays sixth seed Gisela Dulko. The Argentine thrashed Italian Maria Elena Camerin 6-3, 6-0.
Fourth seed Dinara Safina, younger sister of Australian Open champion Marat Safin, edged out Russian compatriot Maria Kirilenko 6-4, 7-6.
Teenager Michaella Krajicek, sister of former Wimbledon champion Richard Krajicek, reached her first WTA Tour quarter-final with a 6-3, 3-6, 6-2 victory over third seed Anabel Medina Garrigues of Spain.
Krajicek, 16, thrilled her home crowd with a mature performance, hitting back after dropping the second set to beat the world number 30 in one hour 43 minutes.
"I'm really happy that I won today because I need more matches, especially on grass," said the Dutchwoman, who will meet American Meghann Shaughnessy in the last eight.
