Djokovic continues winning run, Del Potro out

The top seed, who is trying to join Andre Agassi as a six-times Miami winner, improved his record since the start of 2015 to 105-7, picking up 14 titles along the way.

Just five days after an emphatic victory at Indian Wells, the Serb adjusted well to the steamy conditions in south Florida. He was broken once, in the first set, but broke 21-year-old Edmund four times.

Earlier in the day, Juan Martin del Potro had two surprises -- the first when his scheduled opponent Roger Federer withdrew with illness, and the second when he fell 6-4 6-4 to lucky loser and fellow Argentine Horacio Zeballos.

World number 112 Zeballos did not face a break point en route to his first tour-level win of the year.

Former U.S. Open champion Del Potro, on the comeback trail after missing nearly a year due a left wrist injury, was clearly bothered by the joint.

"He played well,” said del Potro of Zeballos. "He's a lefty, he can play to my backhand easier than anyone else. He played very smart.

"I was suffering a little bit. It was worse than in my first match, but I hope it’s nothing dangerous.

"It’d be a surprise for me to win a match at this moment because I'm not 100 percent yet. But I'm here playing tennis. That's good for me."

Jeremy Chardy of France, the 28th seed, went down 6-4 6-4 to Spaniard Fernando Verdasco.

Briton Andy Murray, Spaniard Rafa Nadal and Japan's Kei Nishikori will be among those in action on Saturday.