Del Potro plots his path back to the top

Juan Martin Del Potro, the only man to break the Grand Slam stranglehold of the world's three top tennis stars since 2005, is closing the gap on the greats but still can't find that championship form.

Defending champion Novak Djokovic ended the Argentine seventh seed's run at the US Open on Thursday with a 6-2, 7-6 (3), 6-4 victory.

"It's not easy when you fire your best weapon and the other guy returns all the serves," Del Potro said. "It's difficult when you have in front of you a warrior. He's playing better and better every day. He's the favorite to win this tournament. I saw him playing at a very high level for the three hours of the match and he has intensity to win all the matches."