Rafael Nadal, Roger Federer, Andy Roddick, watch your backs! There's a new ball boy in town from Argentina and his name is Juan Martin del Potro. Last night when del Potro teared up after besting Federer in the U.S. Open men's finals, our hearts just melted like a pat of butter in the Argentine sun.

Only 20 years old, del Potro sports major talent, but still has the slightly doofy, untarnished look of an innocent. You know, kind of like Michael Phelps did before all that strippers-and-pot unpleasantness! Click through our gallery of del Potro's to-die-for muscles and sexy smile ... plus, some sweet pics of del Potro and Federer to save for the spank bank!