Noren, Karlsson and Van Zyl, who is from South Africa, each turned in a 5-under-par 67 and lead a group of four players, which includes another Swede in Niklas Lemke, by one stroke.
Nine more golfers are at 3-under-par. That includes 22-year pro Robert Karlsson, who is no relation to the co-leader Robert Karlsson -- a 22-year-old amateur.
The amateur Karlsson could well have owned the outright lead but had a double bogey at the par-3, 164-yard 17th hole. However, he had a birdie at No. 18. He was 4-under after eight holes, after a string of three birdies on Nos. 6-8.
Noren also had a double bogey that threatened a strong start. Playing the back nine first, he had five birdies in his first six holes. After four pars, he had a 6 at the par-4 second hole and a bogey at No. 4. He got back into the lead with a birdie at the fifth hole and closed with birdies at 8 and 9.
Van Zyl's round was less dramatic, mixing six birdies and one bogey for his share of the lead.
Swim Week Miami Beach 2014 [PHOTOS]