Second seed Tommy Haas crashed out of the US Clay Court Championships in Houston on Thursday, suffering a straight sets defeat to Ricardas Berankis of Lithuania.
The German veteran -- who had inflicted a shock defeat on world number one Novak Djokovic at the Miami Masters last month -- was sent tumbling out 6-3 6-3 at the River Oaks Country Club.
It was just the second time this year the 35-year-old Haas lost his opening match.
"It started off pretty weird and it didn't really give me that much confidence for the rest of the match," he said. "I felt if I could've held serve in the first game then things would've been a little different."
Berankis said: "I think I had the advantage because for me it was the second match. For the first clay-court matches it's a big advantage. I used it well to get my rhythm."
In other matches on Thursday, Nicolas Almagro continued his dominance of Gael Monfils on clay by rallying past the former world number seven 2-6, 6-0, 6-3 in their second round tie.
Almagro, of Spain, has now won three of five career meetings against the Frenchman, including all three times they have met on the clay surface.
Almagro finished with three aces, one double fault and won 74 percent of his first-serve points in the 85-minute match.
Almagro advances to the third round where he will face Paolo Lorenzi who won an all-Italian duel by beating Flavio Cipolla 7-6 (7/4), 6-1
Last year's Houston runner-up John Isner was also a second-round winner Thursday.
The fifth-seeded six-foot-nine Isner outlasted fellow American Jack Sock 7-5, 6-7 (3/7), 7-6 (7/3) in 2 1/2 hours. The two big servers combined for 28 aces, including 15 from Isner.
Also, Ruben Ramirez Hidalgo ousted sixth-seeded fellow Spaniard Fernando Verdasco 6-3, 6-2 in 67 minutes.
American wild card Rhyne Williams beat Croatian lucky loser Ivo Karlovic 6-4, 6-7 (5/7), 7-6 (7/3). Karlovic lost despite blasting 28 aces to just seven for Williams.