Del Potro warns he's hitting the heights

Juan Martin del Potro said he was playing even better than when he won the 2009 US Open after pushing Novak Djokovic to the limit in a gripping Shanghai Masters final.

The towering Argentine won this month's Japan Open and beat world No 1 Rafael Nadal in the Shanghai semifinals, before coming up just short in a third-set tie-breaker with Djokovic.

But the 1.98 meter del Potro has shown he is primed for another assault on the majors with three titles this year and two appearances in Masters finals.