Juan Martin del Potro wants to turn tennis' Big Four into a quintet in 2013.
The big-hitting Argentine's season ended Sunday when he wasted a one-set lead against Novak Djokovic and lost 4-6, 6-3, 6-2 in the semifinals of the ATP finals.
But his strong end to the year has made Del Potro confident he can again challenge the sport's biggest names for Grand Slam titles next season as he did in 2009 when he won the 2009 U.S. Open before a serious wrist injury.
Del Potro says he's "getting closer every day" to the likes of Djokovic, Roger Federer, Andy Murray and Rafael Nadal. That, he says, could be "my big challenge for next year, my big goal."