The British No 1 wins the Brisbane International, beating Alexandr Dolgopolov, while Del Potro says Djokovic has a target on his back.
Andy Murray warms-up for Australian Open in style
Top seed Andy Murray secured his first title of 2012 in clinical fashion at the ATP Brisbane International with victory over Ukraine's Alexandr Dolgopolov.
The British No 1, under the watchful eye of new coach Ivan Lendl this week, took control of the final with a run of nine straight games en route to a 6-1 6-3 triumph.
Dolgopolov, who seemed to be struggling with a groin problem towards the end of the first set, rallied from 4-0 down in the second set to get back to 4-3, but Murray then raised his game again to close out the match.
Djokovic won the Australian Open, Wimbledon and US Open in 2011 to take the world No 1 ranking while compiling an imperious 70-6 win-loss record that set a new benchmark on the ATP Tour.
He will be the top seed and man to beat at the January 16-29 Australian Open but del Potro, who is rapidly returning to the upper echelons of men's tennis after wrist and shoulder injuries, expected Federer and Nadal to go all out to cut Djokovic down to size.
"I think Roger and Rafa will be going after Novak because they don't want him to repeat the year he just had," former US Open champion del Potro said.
"What he [Djokovic] did, very difficult for him to do again," he added. "I think if someone can do the same, the only three who can do it are Roger, Rafa and Novak. They are the only three who can have the same fantastic year Novak did."
Del Potro is the top seed at the Sydney International, which began in low-key fashion today without any big names in action. The Argentine says he is plotting a return to the top five after falling as far as number 485 in the rankings after the Australian Open last year.
Now at No 11 and feeling fully fit, he is one of the few players who can blast opponents off a court with all the destructive force of Djokovic, Nadal and the more crafty Federer. A beast of a player is stirring. "I'm feeling good," Del Potro said. "Players come to Sydney and Melbourne in different levels of fitness but I have trained at home and I am ready. I am in good shape and want to play many, many matches.
"Always the first tournament of the year is difficult and I need to keep playing points and matches to keep improving my level. My comeback year went better than I expected. If I stay healthy I think I have a good chance to win a lot of matches this year.
"My injuries to my back and my wrist are a thing of the past. I am close to the top 10 again and I want to be there with the biggest names in this sport. "I have many goals this year. I want to play like I did all those years ago."