Seeds Denis Istomin and Robin Haase were among Monday's first-round victors at the $525,000 Estoril Open tennis event.

The fifth-seeded Istomin, of Uzbekistan, handled Frenchman Paul-Henri Mathieu 7-5, 6-1, while the sixth-seeded Dutchman Haase humbled Italian Simone Bolelli 6-3, 6-2 at National Stadium.

One other Day-1 result saw Italian Paolo Lorenzi sneak past Frenchman Edouard Roger-Vasselin 3-6, 7-6 (7-2), 6-4.

The top seeds in Estoril are reigning champion Juan Martin del Potro and sweet-swinging 2007 runner-up Richard Gasquet, who will face Lorenzi in the second round after receiving an opening-round bye.

The former U.S. Open runner-up del Potro beat Spaniard Fernando Verdasco in last year's finale here.

The winner of this clay-court French Open tune-up will claim $95,000.