MIAMI - Andy Murray will have to solve the problem of his patchy play quickly if he hopes to defend his Miami ATP Masters title against a star-studded field. Murray departed Miami last year ranked second in the world after a razor-thin victory over David Ferrer in the final gave him his second Sony Open title. He went on to claim an emotional second Grand Slam title at Wimbledon, but the 26-year-old has yet to reach a final since having back surgery in September and is currently ranked sixth in the world.The Scot was at a loss to explain a third-set collapse against big-serving Canadian Milos Raonic in the fourth round at the Indian Wells Masters last week and admitted his confidence was at low ebb. That will put him at a distinct disadvantage against the likes of world number one Rafael Nadal, who returns to Miami after skipping last year's tournament to rest his troublesome knees. World number two Novak Djokovic also arrives in Florida brimming with confidence, having secured his first title of 2014 with a triumph over a revitalized Roger Federer in the Indian Wells final on Sunday."It was the first final I played this year," Djokovic noted. "It was necessary for my confidence and hopefully I can carry that into Miami and the rest of the season." Djokovic was especially pleased that he came through some tough three-set matches, including rallying from a set down against Croatian Marin Cilic in the fourth round and Federer in the championship contest. Getting through the tense encounters quelled the doubts he'd felt upon arriving Stateside for the two big hardcourt tournaments without a title for the first time in years.Djokovic avenged a loss to Federer in the semi-finals at Dubai in February, but said the Swiss great was clearly a force to be reckoned with now that he has put his injury-marred 2013 campaign behind him. "Roger is playing at a very high level," Djokovic said. "He has more depth on his shots, especially from the backhand side. He gives himself an opportunity to finish with the forehand. He serves well. He just played better than he did in the last 13, 14 months."Federer, who had fallen to eighth in the world, heads into Miami back at number five. He too is returning to Key Biscayne after skipping the tournament last year, and after winning the title in Dubai and reaching the final in Indian Wells in back-to-back events the 17-time Grand Slam champion left himself some wiggle room with regard to playing another tournament so soon. "I will see how I feel over there," Federer said shortly after the Indian Wells final. "Most likely, yes, I will play."Women's world number one Serena Williams returns to defend the title she won last year with a victory over Maria Sharapova in the final. Women's first-round play begins on Tuesday, but the 32 men's and women's seeds all have first-round byes. Williams, owner of 17 Grand Slam titles and a record six Miami trophies, will no doubt be eager to get back on track after her season-opening triumph in Brisbane was followed by a fourth-round loss at the Australian Open and a semi-final loss to France's Alize Cornet at Dubai in February.Sharapova will try to bounce back from a third-round loss to Italian qualifier Camila Giorgi at Indian Wells. The Russian reached her fifth Miami final last year, but has never won the title. China's Australian Open champion Li Na arrives in Florida after a semi-final defeat to eventual champion Flavia Pennetta in Indian Wells. Li struggled with her serve in the California desert thanks to a change in her mechanics, but said she hoped to have the problems ironed out. "Nothing to worry about," Li said. "Should be OK in next tournament."