British number three James Ward could not build on his run through qualifying as he lost to Turkey's Marsel Ilhan in the first round of the Barcelona Open.
The Londoner, 28, had won two matches in qualifying on the clay but went down 7-6 (7-2) 3-6 6-1 against Ilhan, ranked 22 places higher at 84th in the world.
Russian 17-year-old Andrey Rublev, the junior world number one, upset 37th-ranked Fernando Verdasco 7-6 (7-4) 6-3.
"I'm really happy to win against one of the best players on tour," said Rublev.
"It's amazing, I don't even know what to say - I'm just so happy. I tried not to think and just keep showing my best every point. I had nothing to lose."
Japanese top seed Kei Nishikori beat Russia's Teymuraz Gabashvili 6-3 6-4 in his opening match.
Spanish second seed Rafael Nadal, trying to win his ninth Barcelona title, will begin his campaign later in the week against compatriot Nicolas Almagro.