Seeded trio Guillermo Garcia-Lopez, Fernando Verdasco and Vasek Pospisil were all sent packing in the second round of the Topshelf Open in Holland.
Fourth seed Garcia-Lopez was given a bye in the opening round but the Spaniard lost a tight tie-break to world number 196 Marius Copil before going down 7-6 (7/5) 6-4.
The Romanian will next take on Gilles Muller, with the world number 53 from Luxembourg outlasting ninth seed Pospisil, who was defeated 6-4 4-6 7-6 (8/6) in a match that lasted a little over two hours.
"He's a dangerous player," said Muller on his next opponent on the ATP Tour website. "I've played him a couple of times already. He has a huge serve. So I have to be ready to return some bombs.
"Especially on the grass, it's going to be a 50-50 match. With a big serve like that, on grass, he can beat anyone."
Seventh seed Verdasco also tumbled out, the Spaniard losing 7-6 (7/4) 6-3 to home favourite Robin Haase, who will next face Ivo Karlovic, seeded fifth, after the Croatian beat Japan's Tatsuma Ito 7-6 (7/5) 7-6 (7/3).
In the women's event, fifth seed Camila Giorgi was forced to battle for a 6-7 (2/7) 6-2 6-4 against Michaella Krajicek to reach the quarter-finals.
The Italian said after beating the big-serving home hope on the WTA Tour website: "I just had to be patient.
"I waited for my chances, and when it was my time, just get it back. It was a good match."
Third seed CoCo Vandeweghe of the United States won 14 of the final 15 points in a 7-5 6-4 win over Germany's Tatjana Maria.
French seventh seed Kristina Mladenovic battled back from a set down before edging out Japan's Kurumi Nara, 6-7 (4/7) 6-3 6-3, while Kazakhstan's Yaroslava Shvedova eased past Marina Erakovic of New Zealand 6-4 6-4.
Source: PA
