KEY BISCAYNE, Fla. — Rafael Nadal's bid for his first Key Biscayne title has been ended by Juan Martin del Potro.

The 20-year-old Argentine upset the top-ranked Nadal 6-4, 3-6, 7-6 (3) Thursday in the quarterfinals at the Sony Ericsson Open.

Del Potro had lost all nine sets in their four previous matches, but he was buoyed by a home-court advantage, with many transplanted Argentines in the crowd singing "Del-Po" between points.

Victoria Azarenka, a 19-year-old Belarussian, earned a berth in the women's final by beating Svetlana Kuznetsova 6-3, 2-6, 7-5.

The No. 6-seeded del Potro's opponent Friday will be the winner of the last quarterfinal between No. 4 Andy Murray and No. 8 Fernando Verdasco.