MADRID — Novak Djokovic eased past Oscar Hernandez 6-3, 6-3 Wednesday to advance to the third round of the Madrid Open.

The third-seeded Serb fell awkwardly on his right knee on the clay surface at Madrid's new "Magic Box" tennis center early in the second set, but was rarely troubled by his Spanish opponent.

Djokovic never faced a break point in the match, breaking Hernandez once in the first set and twice in the second.

Juan Martin del Potro of Spain advanced when Tomas Berdych was forced to retire with a leg injury.

The Czech player, who won his first title of the year at the BMW Open in Munich on Sunday, retired while trailing 6-2, 4-1.

In the women's event, Victoria Azarenka defeated Peng Shuai 6-4, 6-1, and Vera Dushevina stopped Francesca Schiavone 6-3, 4-6, 6-2.

In later matches, top-ranked Rafael Nadal was to meet Jurgen Melzer, while top-ranked Dinara Safina was to play Li Na.