Two seeds had first-round wins Tuesday: No. 10 Spaniard Nicolas Almagro was leading Viktor Troicki 6-2 when the Serbian retired due to a back injury and No. 16 Spaniard Feliciano Lopez was ahead of Jose Acasuso 5-2 when the Argentine retired due to a stomach problem.
In an opening-round upset, Russian qualifier Mikhail Kukushkin beat 12th-seeded Finn Jarkko Nieminen 6-4, 6-4.
Spaniard Rafael Nadal, this week's top seed, is the three-time defending Barcelona champion. The reigning three-time French Open champ is fresh off his fourth straight Monte Carlo title last week.