Juan Martin del Potro advanced to the second round of the Sony Ericsson Open in Florida on Wednesday, beating Brazil's Ricardo Mello 6-4, 6-4.

Del Potro, the Argentine star who won the 2009 US Open, was limited to three events last year because of a right wrist injury. He has jumped from 257th to 51st in the rankings this year, winning the Delray Beach International last month and reaching the semifinals in San Jose, Memphis and Indian Wells.

"I'm still improving match by match," said del Potro, 18-5 this year. "It's a good signal for my future, for my comeback, and for recovering my game."

James Blake came back to edge US compatriot Michael Russell 3-6, 7-6 (7), 7-6 (3). South African Kevin Anderson also advanced, beating Russia's Nikolay Davydenko 6-4, 6-3.

In women's first-round play, former world No. 1 Dinara Safina of Russia beat Australian Jelena Dokic 6-4, 6-4.

American Bethanie Mattek-Sands celebrated her 26th birthday with a 6-1, 6-4 victory over Sweden's Sofia Arvidsson. Japan's Kimiko Date-Krumm beat Caech Zuzana Ondraskova 6-4, 6-3.