Six-time Grand Slam winner Novak Djokovic claimed his fourth Miami Masters crown with a dominating straight sets win over world number one Rafael Nadal.Second seed Djokovic cruised to a 6-3, 6-3 win in the men's final of the combined ATP and WTA Tour hardcourt tournament on Sunday.Djokovic, who benefitted from two walkovers, didn't drop a set winning his third Miami title in four years and fourth in total to add to triumphs in 2007, 2011, and 2012.