Dinwiddie had the only bogey-free round of the day and is at 6-under 136 after 36 holes. He has a one-stroke lead over Martin Wiegele, a first-round co-leader who shot even-par 71 Friday.
Jamie Elson (67), Mark F. Haastrup (67) and Matt Haines (68) are tied for third at 4-under 138. Colm Moriarty, who was tied with Wiegele for the lead after Thursday's play, shot 2-over 73 and is tied for sixth.
Dinwiddie played the back nine first Friday, opening with four pars before posting three birdies over the next four holes. He had another four consecutive pars before finishing with three birdies over his final six holes, including a birdie on his closing hole. He had a bogey 6 on the ninth hole Thursday.
"It's a very difficult track but I did think the pins were a little easier today -- though maybe that's just because I was playing better," Dinwiddie. "There were still some very tricky holes out there, so I'm delighted to have kept the bogeys off the card today."
Swim Week Miami Beach 2014 [PHOTOS]