Umag, Croatia:Top-seeded David Nalbandian of Argentina tumbled out of the opening round of the $381,000 ATP Croatia Open, losing to qualifier David Ferrer of Spain 6-4, 6-3. In a game played under lightly sprinkling rain, both players struggled with their serves, with four of the six opening games going against the server. Nalbandian, a surprise finalist at Wimbledon this year, was down 4-5 in the first set and serving to stay in the match but Ferrer converted his fourth break point to clinch the set. The 20-year-old Argentine looked to have regained composure at the beginning of the second set, going up 2-1. But Ferrer, a clay court specialist and semifinalist here last season, rallied to win five of the next six games to win the match. "I had some problems with my knee," Nalbandian said, adding he had trouble adjusting to the humid weather conditions at this Adriatic resort after playing in the high altitude levels of Gstaad in Switzerland a few days ago. "But that was not the reason for my loss. Ferrer is a very good player and he played very good tennis today," he said. Croatia's Mario Radic made short work of Austrian Julian Knowle, winning 6-4, 6-3, while Oliver Gross of Germany came from behind to overcome another Austrian, Markus Hipfl, 3-6, 7-6 (10/8), 7-6 (7/5).