New York (Reuters) - American Serena Williams survived a rare bad day on the courts as she beat Spain's Maria Jose Martinez Sanchez to claim a place in the third round of the U.S. Open on Thursday.

The Wimbledon and Olympic champion, an overwhelming favorite for the title, needed 82 minutes to dig out a 6-2 6-4 victory over 30-year-old Martinez Sanchez.

Williams began well enough, winning 12 straight points as she led 4-1 but struggled thereafter, double-faulting six times and making a host of simple mistakes.

Martinez Sanchez could not capitalize, squandering a 2-0 lead in the second set as Williams battled through to face Ekaterina Makerova of Russia.

(Writing by Simon Cambers; Editing by Gene Cherry)