The 30-year-old picked up five strokes in a blistering outward half of 30 before three back-nine birdies were partially offset by bogeys at the 10th and 18th.
While Carlsson was flying high at the top of the leaderboard, world No 9 Justin Rose had to settle for a 72 and fellow Englishman Ian Poulter ballooned to a 76.