The dominant player in men's tennis immediately turned his attention to Miami, where the second ATP Masters event of the season will start next week.

"It's sport," Djokovic said of the end of a streak that had stretched back to October 31. "Now I need a few days off and I'll move on to Miami."

His 17 victories this year included his run to a fourth Australian Open crown -- his sixth Grand Slam title -- and a triumph in Dubai.

The surge was starting to recall the 43-match winning run he put together in the first half of 2011.

From the moment he arrived Stateside from Dubai, Djokovic was in the spotlight -- sitting courtside at a Los Angeles Lakers game and shooting baskets with the NBA stars he so admires.

After mingling with movie stars at a charity exhibition in Los Angeles, he made his way east to the southern California desert, joking that his coaches had complained about his lack of practice time.

Things looked more serious when he was taken to a third set by 36th-ranked Italian Fabio Fognini in his second-round opener.

Djokovic then got off to a slow start in a 7-6 (7/4), 6-1 win over Bulgarian Grigor Dimitrov in the third round, and found himself in a tense second-set tussle with American Sam Querrey before sealing a 6-0, 7-6 (8/6) fourth-round win in a match that didn't get on court until after midnight.

Eighth-seeded Jo-Wilfried Tsonga put up little resistance in the quarter-finals, but in del Potro, Djokovic was up against a former Grand Slam champion riding high after a quarter-final victory over World No. 3 Andy Murray.

"He has a big serve. He moves around the court very well for his height," Djokovic said of del Potro, whose career was interrupted by a wrist injury that required surgery and kept him off the court for most of 2010 -- the year after he won the US Open.

"He uses that forehand as a great weapon. Great running forehand, so he's opening that side. I didn't use my backhand along the line as I usually do. It's one of my best shots. Today it just wasn't there. My backhand generally wasn't there."